Who knows what the methods are for treating hydrogen in chlor-alkali production? Thanks
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This post was last edited by sunjl1981 on 2013-1-6 at 21:11. I’m looking for information on the design of the hydrogen production process in chlor-alkali manufacturing… Thank you all… hcbbs !! hcbbs
This post was last edited by tclvjian on 2011-11-25 at 14:49. I can provide hydrogen mist treatment equipment: fiber bed demister components, as well as design options and equipment for containers (tanks). If you need it at that time, please contact me: 139 5103 9432. Of course, we can also handle chlorine mist and acid mist.
This post was last edited by tclvjian on 2011-11-26 09:49: circulating water washing cooling, compression, low-temperature water cooling, demisting
Here is some information for reference. Article 2: Hydrogen Treatment. Chapter 1: General Introduction. 1. Overview. 1. Hydrogen: Hydrogen, denoted as H2, has a molecular weight of 2.016. At room temperature, it is a colorless, odorless, and flammable gas； Density is 0℃ ； It is 0.08987 g/l at 760 mmHg, with a boiling point of -252.7℃ ； The crystallization temperature is -259.1℃ ； Its specific gravity relative to air is 0.0695 ； Its solubility in water is very low; at standard conditions, the volume of hydrogen gas that dissolves in water is 0.0215. Meanwhile, its solubility in nickel, palladium, and platinum is very high; one volume can dissolve hundreds of volumes of hydrogen. In addition to being used in the synthesis of hydrogen chloride for the production of hydrochloric acid and polyvinyl chloride, another major use of hydrogen is in the hydrogenation of vegetable oils to produce hardened oils. It is also used in tungsten refining, the production of polysilicon, and the hydrogenation of organic compounds. 2. Tasks and methods for hydrogen treatment: The hydrogen gas coming out of the electrolyzer has a temperature slightly lower than that of the electrolyzer itself; it contains saturated water vapor, as well as mist of salts and alkalis. Therefore, cooling and washing are necessary during the production process. After cooling, the hydrogen gas is compressed by a hydrogen compressor to a certain pressure, and then sent to hydrogen storage tanks and the departments that use hydrogen through hydrogen distribution stations. II. Determination of the hydrogen treatment process flow: The saturated wet hydrogen gas coming out of the electrolyzer contains large amounts of water and other gases. Since comprehensive heat utilization is not given sufficient consideration in this design, a direct-process approach is adopted to simplify the process and reduce costs. The selection process involves using electrolysis to produce hydrogen, which then enters a first washing tower after passing through a buffer tank. It is cooled to 50°C in this tower, and then cooled further to 30°C in a second washing tower. After that, it passes through a wire mesh demister, and finally is pumped to the user using a Roots blower. Chapter 2 Process Calculations I. Hydrogen Treatment Process Flow The process flow diagram for hydrogen treatment is shown below; material balance and heat balance calculations are carried out based on this diagram: Figure 2-1 Hydrogen Treatment Process Flow Diagram The saturated wet hydrogen gas coming out of the electrolyzer contains large amounts of water and other gases, which are generally removed using indirect and direct methods to meet the required standards. Given that comprehensive heat utilization is fully considered in this design, the direct process is adopted to simplify the workflow and reduce costs. The selection process involves the hydrogen produced by electrolysis entering a buffer tank before proceeding to a first washing tower; there it is cooled to 50°C, and then it passes through a second washing tower to reach 30°C. After that, it goes through a wire mesh mist eliminator, and finally is pumped to the user using a Roots blower. The utility system uses industrial water; after heat exchange with hydrogen, it enters the tank, and then is pumped back into the utility system for cooling before being reused again. II. Calculation basis: 1. Calculation standard: The production of hydrogen from 1000 kg of 100% NaOH is used as the reference. 2. When the temperature of the hydrogen being processed reaches 80°C, 25 kg of hydrogen is produced for every 1000 kg of 100% NaOH electrolyte; at this temperature, the saturated water vapor content is 205 kg. 3. The previous operating pressure of the compressor was approximately 1 absolute atmosphere (0 kg/cm2). 4. Hydrogen purity: 98%. 5. The electrolyzed hydrogen is washed in two stages, with the cooling temperature reduced from 80°C to 30°C. 6. The relevant data are as follows: Table 2-1 Relevant Thermodynamic Data. Material and Item, Unit: Temperature in °C – 80, 50, 30. Specific heat of hydrogen, in kcal/kg•°C: 3.439, 3.421, 3.409. Specific enthalpy of water vapor, in kcal/kg: 631.4, 619.1, 610.6. Specific heat of other gases (air), in kcal/kg•°C: 0.244, 0.243, 0.242. Saturated vapor pressure of water, in kcal/cm² (absolute): 0.483, 0.1258, 0.0433. 7. The materials entering the hydrogen system (based on 1000 kg of 100% NaOH as a reference): Hydrogen: 12.5 kmol (25 kg); Water vapor: 11.39 kmol (205 kg); Other gases: × = 0.255 kmol (7.39 kg). Other impurities are not considered. III. Process Calculations (I) Single-stage Washing Cooling Tower 1. Calculation Basis: The temperature of hydrogen in the single-stage cooling tower decreases from 80°C to 50°C; the calculation is based on the production of hydrogen from 1000 kg of 100% NaOH. 2. Material Balance: ⑴ Let WL be the amount of water condensed in the hydrogen. Using Dalton’s law of partial pressures, an equation is established: = Solving this equation gives WL1 = 172 (kg). Since the solubility of gases in water is very low, this value is ignored. Then the composition of the gas exiting the tower is as follows: Hydrogen: 12.5 kmol (25 kg); Water vapor: 1.833 kmol (205 – 172 = 33 kg); Other gases: 0.255 kmol (7.39 kg).
(2) Material balance table
a. Using 1000 kg of 100% NaOH for hydrogen production as the calculation basis
Table 2-2: Material balance table for the first washing and cooling tower
| Name | Inflow to first washing and cooling tower (kg) | Outflow from first washing and cooling tower (kg) |
|------|---------------------------------------------------|---------------------------------------------------|
| Hydrogen | 25 | 25 |
| Water vapor | 205 | 33 |
| Other gases | 7.39 | 7.39 |
| Water | 172 | |
| Total | 237.39 | 237.39 |
b. Overall material balance
Table 2-3: Overall material balance table for the first washing and cooling tower
| Name | Inflow to first washing and cooling tower (kg) | Outflow from first washing and cooling tower (kg) |
|------|---------------------------------------------------|---------------------------------------------------|
| Hydrogen | 5,000,000 | 5,000,000 |
| Water vapor | 41,000,000 | 6,600,000 |
| Other gases | 1,478,000 | 1,478,000 |
| Water | 34,400,000 | |
| Total | 47,478,000 | 47,478,000 |
3. Heat balance
(1) Heat brought in by the gas entering the tower:
Q1 = 80 × 25 × 3.439 = 6,878 kcal
Q2 = 205 × 631.4 = 129,437 kcal
Q3 = 80 × 0.244 × 7.39 = 144 kcal
(2) Heat taken away by the cooling water:
Assuming the volume of cooling water is WL2 kg, with a temperature of 25°C; the temperature of the water exiting the tower is 50°C. Then the volume of water exiting the tower is WL2 + 172.
Heat brought in by the cooling water: Q4 = WL2 × 25
Heat taken away by the cooling water: Q5 = (WL2 + 172) × 50
(3) Heat taken away by the gas exiting the tower:
Q6 = 50 × 25 × 3.421 = 4,276 kcal
Q7 = 33 × 619.1 = 20,430 kcal
Q8 = 50 × 7.39 × 0.243 = 90 kcal
(4) Ignoring heat losses:
Q_in = Q_out
Therefore, Q1 + Q2 + Q3 + Q4 = Q5 + Q6 + Q7 + Q8
6,878 + 129,437 + 144 + 25 × WL2 = (WL2 + 172) × 50 + 4,276 + 20,430 + 90
Thus, WL2 = 4,122.52 kg
That is, the amount of water entering the system is 4,122.52 kg, while the amount of water exiting the system is 4,122.52 + 172 = 4,294.52 kg.
Heat brought in by the cooling water: 4,122.52 × 25 = 103,063 kcal
Heat taken away by the cooling water: (4,122.52 + 172) × 50 = 214,726 kcal
(5) Heat balance table
Table 2-4: Heat balance table for the first washing and cooling tower
| Input/Output | Material name | Quantity (kg) | Heat (kcal) |
|---------------|---------------|----------------|--------------|
| Input | Hydrogen | 25 | 6,878 |
| | Water vapor | 205 | 129,437 |
| Output | Hydrogen | 25 | 4,276 |
| | Water vapor | 33 | 20,430 |
| | Other gases | 7.39 | 144 |
| | Other gases | 7.39 | 90 |
| Input | Cooling water | 4,122.52 | 103,063 |
| Output | Cooling water | 4,294.52 | 214,726 |
| Total | | | 239,522 |
| | | | 43,599.1 |
(II) Second washing and cooling tower
1. Calculation basis
(1) The temperature of the electrolyzed hydrogen is reduced from 50°C to 30°C through two stages of washing and cooling. ⑵ Hydrogen purity: 98%
2. Material balance
(1) The temperature at the outlet of hydrogen from the two-stage scrubbing and cooling tower is 30°C; thus, the amount of condensed water is WL3. Similarly, using Dalton’s law of partial pressures, we can set up an equation: = Solving this yields WL3 = 22.61 kg. Therefore, the composition of the gas exiting the tower is as follows:
Hydrogen: 12.5 kmol (25 kg)
Water vapor: 0.577 kmol (33 – 22.61 = 10.39 kg)
Other gases: 0.255 kmol (7.39 kg)
(2) The proportion of hydrogen in the gas exiting the tower is 93.76%; the percentage of hydrogen in dry gas is 98%.
(3) Material balance table
a. Using 1000 kg of 100% NaOH as the basis for calculation:
Table 2-5: Material balance table for the two-stage scrubbing and cooling tower
| Substance | Input to tower (kg) | Output from tower (kg) |
|-----------|-------------------|----------------------|
| Hydrogen | 25 | 25 |
| Water vapor | 33 | 10.39 |
| Other gases | 7.39 | 7.39 |
| Water | 22.61 | — |
| Total | 65.39 | 65.39 |
b. Overall material balance:
Table 2-6: Overall material balance table for the two-stage scrubbing and cooling tower
| Substance | Input to tower (kg) | Output from tower (kg) |
|-----------|-------------------|----------------------|
| Hydrogen | 5,000,000 | 5,000,000 |
| Water vapor | 6,600,000 | 2,078,000 |
| Other gases | 1,478,000 | 1,478,000 |
| Water | 4,522,000 | — |
| Total | 13,078,000 | 13,078,000 |
3. Heat balance
(1) Heat carried away by gases:
Q6 = 4,276 kcal; Q7 = 20,433 kcal; Q8 = 90 kcal
(2) Heat carried away by gases:
Q9 = 30 × 25 × 3.049 = 2,557 kcal;
Q10 = 10.39 × 610.6 = 6,344 kcal;
Q11 = 30 × 7.39 × 0.242 = 54 kcal
(3) Heat carried away by cooling water:
Let WL4 be the mass of cooling water entering the system; its temperature is 25°C, while the temperature at the tower outlet is 30°C. Thus, the total mass of water exiting the tower is WL4 + WL2 = WL4 + 22.61 kg.
Heat brought in by incoming water: Q13 = WL4 × 25
Heat carried away by outgoing water: Q12 = (WL4 + 22.61) × 30
(4) Ignoring heat losses, we have:
Q_in = Q_out
Thus:
2,557 + 6,344 + 54 + (WL4 + 22.61) × 30 = 4,276 + 20,430 + 90 + WL4 × 25
Solving this gives WL4 = 3,032.54 kg. Therefore, the mass of cooling water entering the tower is 3,032.54 kg, while the mass exiting the tower is 3,032.54 + 22.61 = 3,055.15 kg.
Heat brought in by incoming water: 3,032.54 × 25 = 75,813.5 kcal
Heat carried away by outgoing water: (3,032.54 + 22.61) × 30 = 91,654.5 kcal
(5) Heat balance table:
Table 2-7: Heat balance table for the two-stage scrubbing and cooling tower
| Input | Output |
|-------|--------|
| Substance | Quantity (kg) | Heat (kcal) | Substance | Quantity (kg) | Heat (kcal) |
| Hydrogen | 25 | 6,878 | Hydrogen | 2.5 | 4,276 |
| Water vapor | 33 | 129,437 | Water vapor | 33 | 20,430 |
| Other gases | 7.39 | 144 | Other gases | 7.39 | 90 |
| Cooling water | 4,122.52 | 103,063 | Cooling water | 4,294.52 | 214,726 |
| Total | 4,337.41 | 239,522 | Total | 4,337.41 | 239,522 |
Chapter 3: Design and selection of main equipment
I. Single-stage scrubbing tower
1. Gas flow rate through the tower:
The temperature of gas entering the tower is 80°C, with operating pressure at 1 atmosphere. The total number of moles of gas is:
(12.5 + 11.39 + 0.255) × 26.52 = 640.33 kmol/h
Hence, the volume of gas is:
V = 22.4 × 640.33 × 1 = 18,546.58 m³/h
The total number of moles of gas exiting the tower is:
(12.5 + 1.833 + 0.255) × 26.52 = 386.87 kmol/h
Thus, the volume of gas exiting the tower is:
V = 22.4 × 38876 × 1 = 10,253.05 m³/h
The average gas volume is:
V_avg = 14,399.82 m³/h
2. Diameter of the tower:
Assuming an empty-tower velocity of 0.3 m/s, the diameter D is calculated as:
D = 4.12 m
Therefore, the tower diameter is taken as 4.2 m.
3. Determination and arrangement of nozzles for brine delivery:
Assuming the water supply pressure is 0.2 MPa, and considering possible clogging due to scale formation, the nozzle diameter is set at 3.5 mm. Based on tables, the water flow rate per nozzle is approximately 360 kg/h. Given that 109.33 tons/hour of cooling water at 25°C is required, the total number of nozzles needed is:
n = 303.69
To account for potential clogging issues, 400 nozzles are used instead. 4. Determination of tower height: The nozzles are arranged in 7 layers. There are 50 nozzles facing upward in the lower layer, 35 nozzles facing downward in the upper layer. In the middle 5 layers, there are 60 nozzles per layer, arranged offset from those in the upper and lower layers, spraying water downward. The spacing between pipes is 800 mm; this value increases to 1000 mm in the upper part due to the need for a degassing chamber, and to 2000 mm in the lower part due to the presence of air inlets. Thus, the total tower height is: H = 1000 + 2000 + 7 × 800 = 8600 mm.
5. Selection of pipe diameter: The gas flow velocity inside the pipes is set at 5 m/s. The flow rate of gas entering the tower is 18546.58 m³/h, which equals 5.15 m³/h. Therefore, the diameter of the pipe for gas entering the tower, d1, is 1200 mm. Similarly, the diameter of the pipe for gas leaving the tower is calculated as follows: The flow rate of gas leaving the tower is 10253.05 m³/h, or 2.85 m³/s. Hence, d2 = 0.85 m, or 850 mm. For the cooling water inlet, with a flow velocity of 2 m/s, the diameter d3 is calculated to be 0.139 m; it is chosen to be 150 mm.
II. Two-stage washing tower
1. Gas flow rate through the tower: V = 10253.05 m³/h. The volume of gas leaving the tower is… The temperature of the gas leaving the tower is 30°C, and the operating pressure is approximately 1 atmosphere. Therefore, the total molar amount of gas leaving the tower is: (12.5 + 0.577 + 0.255) × 26.52 = 353.565 kmol/h. V2 = 22.4 × 353.565 × 1 = 8790.17; this value further becomes 9521.61.
2. Determination of tower diameter: Using actual production data, the empty-tower velocity is set at 0.3 m/s. Thus, D = 3.35 m, and the tower diameter is chosen to be 3500 mm.
3. Number of nozzles: Assuming the water supply pressure is 0.2 Mpa, and considering potential blockage by scale, the nozzle diameter is set at 2.5 mm. Based on tables, the water spray rate is 280 kg/h. Using mass balance calculations, the required number of nozzles is 299.04. Considering distribution issues and possible blockages, 350 nozzles are selected.
4. Determination of tower height: The nozzles are arranged in 7 layers. There are 30 nozzles facing downward in the upper layer, 55 nozzles per layer in the middle 5 layers, arranged offset from those in the upper and lower layers, spraying water downward. There are 45 nozzles facing upward in the lower layer. The spacing between pipes is 800 mm; this value increases to 1000 mm in the upper part due to the need for a degassing chamber, and to 2000 mm in the lower part due to the presence of air inlets. Thus, the total tower height is: H = 1000 + 2000 + 7 × 800 = 8600 mm.
5. Selection of pipe diameters: The diameter of the pipe for gas entering the tower, d1, and d2, is 850 mm. The diameter of the pipe for gas leaving the tower is 0.789 m; it is chosen to be 800 mm. For the cooling water inlet, with a flow velocity of 2 m/s, the diameter d6 is calculated to be 0.122 m; it is chosen to be 130 mm.
III. Calculation of main pipe diameters
1. Diameter of the hydrogen gas pipe entering the system: D1 = d1 = 1200 mm.
2. Diameter of the hydrogen gas pipe after compression: With a flow velocity of 12 m/s, D2 = 0.509 m; rounded up to 530 mm.
3. Diameter of the pipe for water at 25°C entering the system: D3 = 0.185 m; rounded up to 200 mm.
4. Diameter of the pipe for cooling water leaving the system: D4 = 0.817 m; rounded up to 200 mm.
IV. Hydrogen delivery equipment: Since the hourly hydrogen delivery volume is 8790.17 m³/h, or 146.5 m³/min, and assuming an efficiency of 80%, the capacity of the hydrogen delivery equipment should be 183.13 m³/min. If three units are used in parallel with an efficiency of 60% each, then each unit’s capacity would be 101.74 m³/min. Four TR series two-stage Roots blowers are selected, with a flow range of 2.61–207 m³/min and a pressure increase of 9.8–196 Kpa.
V. Water delivery pumps: The water flow rate from the circulation tank is (113.89 + 84.33) = 198.22 m³/h. Assuming a head loss and resistance of 20 m (actual values depend on the actual pipeline resistance), according to the “Chemical Process Design Handbook” P1-72, the parameters for the 150F-35 type corrosion-resistant centrifugal pump are as follows: Flow rate: 234 m³/h, Head: 29.7 m, Motor power: 30 KW, Shaft power: 25.2 KW. Since the hydrogen gas produced by electrolysis contains a certain amount of alkaline mist, which makes the circulating water alkaline after washing, two 150F-35 type pumps are selected, one in operation and one as a backup. VI. Liquid-seal circulation tank: According to the design specifications, the distance between the first and second stage scrubbers is 1.5 m, while the distance between the surrounding walls is 0.8 m. Therefore, the length of the liquid-seal circulation tank is: 0.8×2 + 3.6 + 3.0 + 1.5 = 9.7 m, which is rounded up to 10 m. Thus, the distance between the scrubbers should be increased from 1.5 m to 1.8 m. The width is 0.8×2 + 3.6 = 5.2 m. The depth, which is also the height, is determined based on the water volume required for half an hour; hence, H = 1.91 m, rounded up to 2 m. The dimensions of the circulation tank are therefore 10,000 × 5,200 × 2,000.
VII. Hydrogen buffer tank: Based on the volume of gas exiting the scrubbers, the volume V = 2.44 m³/s. After rounding, the dimensions of the equipment are Φ1500×1900.
List of main equipment:
| Serial No. | Equipment Location | Equipment Name | Specifications | Quantity | Unit |
| 1 | E-1001 | Titanium cooler | Φ700×10,000 | 2 | units |
| 2 | V-1003 | Demister | Φ700×900 | 2 | units |
| 3 | T-1001 | Sulfuric acid drying tower I | Dg=1200 | 1 | unit |
| 4 | T-1002 | Sulfuric acid drying tower II | Dg=900 | 1 | unit |
| 5 | T-101-1 | First-stage scrubber | Dg=4,200 | 1 | unit |
| 6 | T-101-2 | Second-stage scrubber | Dg=3,500 | 1 | unit |
| 7 | P-101 | Circulation water pump | 150F-35 | 2 | units |
| 8 | C-101 | Roots blower, TR type | – | 4 | units |
| 9 | V-101 | Hydrogen buffer tank | Φ1500×1900 | 1 | unit |
(2) Material balance table
a. Using 1000 kg of 100% NaOH for hydrogen production as the calculation basis
Table 2-2: Material balance table for the first washing and cooling tower
| Name | Inflow to first washing and cooling tower (kg) | Outflow from first washing and cooling tower (kg) |
|------|---------------------------------------------------|---------------------------------------------------|
| Hydrogen | 25 | 25 |
| Water vapor | 205 | 33 |
| Other gases | 7.39 | 7.39 |
| Water | 172 | |
| Total | 237.39 | 237.39 |
b. Overall material balance
Table 2-3: Overall material balance table for the first washing and cooling tower
| Name | Inflow to first washing and cooling tower (kg) | Outflow from first washing and cooling tower (kg) |
|------|---------------------------------------------------|---------------------------------------------------|
| Hydrogen | 5,000,000 | 5,000,000 |
| Water vapor | 41,000,000 | 6,600,000 |
| Other gases | 1,478,000 | 1,478,000 |
| Water | 34,400,000 | |
| Total | 47,478,000 | 47,478,000 |
3. Heat balance
(1) Heat brought in by the gas entering the tower:
Q1 = 80 × 25 × 3.439 = 6,878 kcal
Q2 = 205 × 631.4 = 129,437 kcal
Q3 = 80 × 0.244 × 7.39 = 144 kcal
(2) Heat taken away by the cooling water:
Assuming the volume of cooling water is WL2 kg, with a temperature of 25°C; the temperature of the water exiting the tower is 50°C. Then the volume of water exiting the tower is WL2 + 172.
Heat brought in by the cooling water: Q4 = WL2 × 25
Heat taken away by the cooling water: Q5 = (WL2 + 172) × 50
(3) Heat taken away by the gas exiting the tower:
Q6 = 50 × 25 × 3.421 = 4,276 kcal
Q7 = 33 × 619.1 = 20,430 kcal
Q8 = 50 × 7.39 × 0.243 = 90 kcal
(4) Ignoring heat losses:
Q_in = Q_out
Therefore, Q1 + Q2 + Q3 + Q4 = Q5 + Q6 + Q7 + Q8
6,878 + 129,437 + 144 + 25 × WL2 = (WL2 + 172) × 50 + 4,276 + 20,430 + 90
Thus, WL2 = 4,122.52 kg
That is, the amount of water entering the system is 4,122.52 kg, while the amount of water exiting the system is 4,122.52 + 172 = 4,294.52 kg.
Heat brought in by the cooling water: 4,122.52 × 25 = 103,063 kcal
Heat taken away by the cooling water: (4,122.52 + 172) × 50 = 214,726 kcal
(5) Heat balance table
Table 2-4: Heat balance table for the first washing and cooling tower
| Input/Output | Material name | Quantity (kg) | Heat (kcal) |
|---------------|---------------|----------------|--------------|
| Input | Hydrogen | 25 | 6,878 |
| | Water vapor | 205 | 129,437 |
| Output | Hydrogen | 25 | 4,276 |
| | Water vapor | 33 | 20,430 |
| | Other gases | 7.39 | 144 |
| | Other gases | 7.39 | 90 |
| Input | Cooling water | 4,122.52 | 103,063 |
| Output | Cooling water | 4,294.52 | 214,726 |
| Total | | | 239,522 |
| | | | 43,599.1 |
(II) Second washing and cooling tower
1. Calculation basis
(1) The temperature of the electrolyzed hydrogen is reduced from 50°C to 30°C through two stages of washing and cooling. ⑵ Hydrogen purity: 98%
2. Material balance
(1) The temperature at the outlet of hydrogen from the two-stage scrubbing and cooling tower is 30°C; thus, the amount of condensed water is WL3. Similarly, using Dalton’s law of partial pressures, we can set up an equation: = Solving this yields WL3 = 22.61 kg. Therefore, the composition of the gas exiting the tower is as follows:
Hydrogen: 12.5 kmol (25 kg)
Water vapor: 0.577 kmol (33 – 22.61 = 10.39 kg)
Other gases: 0.255 kmol (7.39 kg)
(2) The proportion of hydrogen in the gas exiting the tower is 93.76%; the percentage of hydrogen in dry gas is 98%.
(3) Material balance table
a. Using 1000 kg of 100% NaOH as the basis for calculation:
Table 2-5: Material balance table for the two-stage scrubbing and cooling tower
| Substance | Input to tower (kg) | Output from tower (kg) |
|-----------|-------------------|----------------------|
| Hydrogen | 25 | 25 |
| Water vapor | 33 | 10.39 |
| Other gases | 7.39 | 7.39 |
| Water | 22.61 | — |
| Total | 65.39 | 65.39 |
b. Overall material balance:
Table 2-6: Overall material balance table for the two-stage scrubbing and cooling tower
| Substance | Input to tower (kg) | Output from tower (kg) |
|-----------|-------------------|----------------------|
| Hydrogen | 5,000,000 | 5,000,000 |
| Water vapor | 6,600,000 | 2,078,000 |
| Other gases | 1,478,000 | 1,478,000 |
| Water | 4,522,000 | — |
| Total | 13,078,000 | 13,078,000 |
3. Heat balance
(1) Heat carried away by gases:
Q6 = 4,276 kcal; Q7 = 20,433 kcal; Q8 = 90 kcal
(2) Heat carried away by gases:
Q9 = 30 × 25 × 3.049 = 2,557 kcal;
Q10 = 10.39 × 610.6 = 6,344 kcal;
Q11 = 30 × 7.39 × 0.242 = 54 kcal
(3) Heat carried away by cooling water:
Let WL4 be the mass of cooling water entering the system; its temperature is 25°C, while the temperature at the tower outlet is 30°C. Thus, the total mass of water exiting the tower is WL4 + WL2 = WL4 + 22.61 kg.
Heat brought in by incoming water: Q13 = WL4 × 25
Heat carried away by outgoing water: Q12 = (WL4 + 22.61) × 30
(4) Ignoring heat losses, we have:
Q_in = Q_out
Thus:
2,557 + 6,344 + 54 + (WL4 + 22.61) × 30 = 4,276 + 20,430 + 90 + WL4 × 25
Solving this gives WL4 = 3,032.54 kg. Therefore, the mass of cooling water entering the tower is 3,032.54 kg, while the mass exiting the tower is 3,032.54 + 22.61 = 3,055.15 kg.
Heat brought in by incoming water: 3,032.54 × 25 = 75,813.5 kcal
Heat carried away by outgoing water: (3,032.54 + 22.61) × 30 = 91,654.5 kcal
(5) Heat balance table:
Table 2-7: Heat balance table for the two-stage scrubbing and cooling tower
| Input | Output |
|-------|--------|
| Substance | Quantity (kg) | Heat (kcal) | Substance | Quantity (kg) | Heat (kcal) |
| Hydrogen | 25 | 6,878 | Hydrogen | 2.5 | 4,276 |
| Water vapor | 33 | 129,437 | Water vapor | 33 | 20,430 |
| Other gases | 7.39 | 144 | Other gases | 7.39 | 90 |
| Cooling water | 4,122.52 | 103,063 | Cooling water | 4,294.52 | 214,726 |
| Total | 4,337.41 | 239,522 | Total | 4,337.41 | 239,522 |
Chapter 3: Design and selection of main equipment
I. Single-stage scrubbing tower
1. Gas flow rate through the tower:
The temperature of gas entering the tower is 80°C, with operating pressure at 1 atmosphere. The total number of moles of gas is:
(12.5 + 11.39 + 0.255) × 26.52 = 640.33 kmol/h
Hence, the volume of gas is:
V = 22.4 × 640.33 × 1 = 18,546.58 m³/h
The total number of moles of gas exiting the tower is:
(12.5 + 1.833 + 0.255) × 26.52 = 386.87 kmol/h
Thus, the volume of gas exiting the tower is:
V = 22.4 × 38876 × 1 = 10,253.05 m³/h
The average gas volume is:
V_avg = 14,399.82 m³/h
2. Diameter of the tower:
Assuming an empty-tower velocity of 0.3 m/s, the diameter D is calculated as:
D = 4.12 m
Therefore, the tower diameter is taken as 4.2 m.
3. Determination and arrangement of nozzles for brine delivery:
Assuming the water supply pressure is 0.2 MPa, and considering possible clogging due to scale formation, the nozzle diameter is set at 3.5 mm. Based on tables, the water flow rate per nozzle is approximately 360 kg/h. Given that 109.33 tons/hour of cooling water at 25°C is required, the total number of nozzles needed is:
n = 303.69
To account for potential clogging issues, 400 nozzles are used instead. 4. Determination of tower height: The nozzles are arranged in 7 layers. There are 50 nozzles facing upward in the lower layer, 35 nozzles facing downward in the upper layer. In the middle 5 layers, there are 60 nozzles per layer, arranged offset from those in the upper and lower layers, spraying water downward. The spacing between pipes is 800 mm; this value increases to 1000 mm in the upper part due to the need for a degassing chamber, and to 2000 mm in the lower part due to the presence of air inlets. Thus, the total tower height is: H = 1000 + 2000 + 7 × 800 = 8600 mm.
5. Selection of pipe diameter: The gas flow velocity inside the pipes is set at 5 m/s. The flow rate of gas entering the tower is 18546.58 m³/h, which equals 5.15 m³/h. Therefore, the diameter of the pipe for gas entering the tower, d1, is 1200 mm. Similarly, the diameter of the pipe for gas leaving the tower is calculated as follows: The flow rate of gas leaving the tower is 10253.05 m³/h, or 2.85 m³/s. Hence, d2 = 0.85 m, or 850 mm. For the cooling water inlet, with a flow velocity of 2 m/s, the diameter d3 is calculated to be 0.139 m; it is chosen to be 150 mm.
II. Two-stage washing tower
1. Gas flow rate through the tower: V = 10253.05 m³/h. The volume of gas leaving the tower is… The temperature of the gas leaving the tower is 30°C, and the operating pressure is approximately 1 atmosphere. Therefore, the total molar amount of gas leaving the tower is: (12.5 + 0.577 + 0.255) × 26.52 = 353.565 kmol/h. V2 = 22.4 × 353.565 × 1 = 8790.17; this value further becomes 9521.61.
2. Determination of tower diameter: Using actual production data, the empty-tower velocity is set at 0.3 m/s. Thus, D = 3.35 m, and the tower diameter is chosen to be 3500 mm.
3. Number of nozzles: Assuming the water supply pressure is 0.2 Mpa, and considering potential blockage by scale, the nozzle diameter is set at 2.5 mm. Based on tables, the water spray rate is 280 kg/h. Using mass balance calculations, the required number of nozzles is 299.04. Considering distribution issues and possible blockages, 350 nozzles are selected.
4. Determination of tower height: The nozzles are arranged in 7 layers. There are 30 nozzles facing downward in the upper layer, 55 nozzles per layer in the middle 5 layers, arranged offset from those in the upper and lower layers, spraying water downward. There are 45 nozzles facing upward in the lower layer. The spacing between pipes is 800 mm; this value increases to 1000 mm in the upper part due to the need for a degassing chamber, and to 2000 mm in the lower part due to the presence of air inlets. Thus, the total tower height is: H = 1000 + 2000 + 7 × 800 = 8600 mm.
5. Selection of pipe diameters: The diameter of the pipe for gas entering the tower, d1, and d2, is 850 mm. The diameter of the pipe for gas leaving the tower is 0.789 m; it is chosen to be 800 mm. For the cooling water inlet, with a flow velocity of 2 m/s, the diameter d6 is calculated to be 0.122 m; it is chosen to be 130 mm.
III. Calculation of main pipe diameters
1. Diameter of the hydrogen gas pipe entering the system: D1 = d1 = 1200 mm.
2. Diameter of the hydrogen gas pipe after compression: With a flow velocity of 12 m/s, D2 = 0.509 m; rounded up to 530 mm.
3. Diameter of the pipe for water at 25°C entering the system: D3 = 0.185 m; rounded up to 200 mm.
4. Diameter of the pipe for cooling water leaving the system: D4 = 0.817 m; rounded up to 200 mm.
IV. Hydrogen delivery equipment: Since the hourly hydrogen delivery volume is 8790.17 m³/h, or 146.5 m³/min, and assuming an efficiency of 80%, the capacity of the hydrogen delivery equipment should be 183.13 m³/min. If three units are used in parallel with an efficiency of 60% each, then each unit’s capacity would be 101.74 m³/min. Four TR series two-stage Roots blowers are selected, with a flow range of 2.61–207 m³/min and a pressure increase of 9.8–196 Kpa.
V. Water delivery pumps: The water flow rate from the circulation tank is (113.89 + 84.33) = 198.22 m³/h. Assuming a head loss and resistance of 20 m (actual values depend on the actual pipeline resistance), according to the “Chemical Process Design Handbook” P1-72, the parameters for the 150F-35 type corrosion-resistant centrifugal pump are as follows: Flow rate: 234 m³/h, Head: 29.7 m, Motor power: 30 KW, Shaft power: 25.2 KW. Since the hydrogen gas produced by electrolysis contains a certain amount of alkaline mist, which makes the circulating water alkaline after washing, two 150F-35 type pumps are selected, one in operation and one as a backup. VI. Liquid-seal circulation tank: According to the design specifications, the distance between the first and second stage scrubbers is 1.5 m, while the distance between the surrounding walls is 0.8 m. Therefore, the length of the liquid-seal circulation tank is: 0.8×2 + 3.6 + 3.0 + 1.5 = 9.7 m, which is rounded up to 10 m. Thus, the distance between the scrubbers should be increased from 1.5 m to 1.8 m. The width is 0.8×2 + 3.6 = 5.2 m. The depth, which is also the height, is determined based on the water volume required for half an hour; hence, H = 1.91 m, rounded up to 2 m. The dimensions of the circulation tank are therefore 10,000 × 5,200 × 2,000.
VII. Hydrogen buffer tank: Based on the volume of gas exiting the scrubbers, the volume V = 2.44 m³/s. After rounding, the dimensions of the equipment are Φ1500×1900.
List of main equipment:
| Serial No. | Equipment Location | Equipment Name | Specifications | Quantity | Unit |
| 1 | E-1001 | Titanium cooler | Φ700×10,000 | 2 | units |
| 2 | V-1003 | Demister | Φ700×900 | 2 | units |
| 3 | T-1001 | Sulfuric acid drying tower I | Dg=1200 | 1 | unit |
| 4 | T-1002 | Sulfuric acid drying tower II | Dg=900 | 1 | unit |
| 5 | T-101-1 | First-stage scrubber | Dg=4,200 | 1 | unit |
| 6 | T-101-2 | Second-stage scrubber | Dg=3,500 | 1 | unit |
| 7 | P-101 | Circulation water pump | 150F-35 | 2 | units |
| 8 | C-101 | Roots blower, TR type | – | 4 | units |
| 9 | V-101 | Hydrogen buffer tank | Φ1500×1900 | 1 | unit |
Here is some information for reference. Article 2: Hydrogen Treatment. Chapter 1: General Introduction. 1. Overview. 1. Hydrogen: Hydrogen, denoted as H2, has a molecular weight of 2.016. At room temperature, it is a colorless, odorless, and flammable gas； Density is 0℃ ； It is 0.08987 g/l at 760 mmHg, with a boiling point of -252.7℃ ； The crystallization temperature is -259.1℃ ； Its specific gravity relative to air is 0.0695 ； Its solubility in water is very low; at standard conditions, the volume of hydrogen gas that dissolves in water is 0.0215. Meanwhile, its solubility in nickel, palladium, and platinum is very high; one volume can dissolve hundreds of volumes of hydrogen. In addition to being used in the synthesis of hydrogen chloride for the production of hydrochloric acid and polyvinyl chloride, another major use of hydrogen is in the hydrogenation of vegetable oils to produce hardened oils. It is also used in tungsten refining, the production of polysilicon, and the hydrogenation of organic compounds. 2. Tasks and methods for hydrogen treatment: The hydrogen gas coming out of the electrolyzer has a temperature slightly lower than that of the electrolyzer itself; it contains saturated water vapor, as well as mist of salts and alkalis. Therefore, cooling and washing are necessary during the production process. After cooling, the hydrogen gas is compressed by a hydrogen compressor to a certain pressure, and then sent to hydrogen storage tanks and the departments that use hydrogen through hydrogen distribution stations. II. Determination of the hydrogen treatment process flow: The saturated wet hydrogen gas coming out of the electrolyzer contains large amounts of water and other gases. Since comprehensive heat utilization is not given sufficient consideration in this design, a direct-process approach is adopted to simplify the process and reduce costs. The selection process involves using electrolysis to produce hydrogen, which then enters a first washing tower after passing through a buffer tank. It is cooled to 50°C in this tower, and then cooled further to 30°C in a second washing tower. After that, it passes through a wire mesh demister, and finally is pumped to the user using a Roots blower. Chapter 2 Process Calculations I. Hydrogen Treatment Process Flow The process flow diagram for hydrogen treatment is shown below; material balance and heat balance calculations are carried out based on this diagram: Figure 2-1 Hydrogen Treatment Process Flow Diagram The saturated wet hydrogen gas coming out of the electrolyzer contains large amounts of water and other gases, which are generally removed using indirect and direct methods to meet the required standards. Given that comprehensive heat utilization is fully considered in this design, the direct process is adopted to simplify the workflow and reduce costs. The selection process involves the hydrogen produced by electrolysis entering a buffer tank before proceeding to a first washing tower; there it is cooled to 50°C, and then it passes through a second washing tower to reach 30°C. After that, it goes through a wire mesh mist eliminator, and finally is pumped to the user using a Roots blower. The utility system uses industrial water; after heat exchange with hydrogen, it enters the tank, and then is pumped back into the utility system for cooling before being reused again. II. Calculation basis: 1. Calculation standard: The production of hydrogen from 1000 kg of 100% NaOH is used as the reference. 2. When the temperature of the hydrogen being processed reaches 80°C, 25 kg of hydrogen is produced for every 1000 kg of 100% NaOH electrolyte; at this temperature, the saturated water vapor content is 205 kg. 3. The previous operating pressure of the compressor was approximately 1 absolute atmosphere (0 kg/cm2). 4. Hydrogen purity: 98%. 5. The electrolyzed hydrogen is washed in two stages, with the cooling temperature reduced from 80°C to 30°C. 6. The relevant data are as follows: Table 2-1 Relevant Thermodynamic Data. Material and Item, Unit: Temperature in °C – 80, 50, 30. Specific heat of hydrogen, in kcal/kg•°C: 3.439, 3.421, 3.409. Specific enthalpy of water vapor, in kcal/kg: 631.4, 619.1, 610.6. Specific heat of other gases (air), in kcal/kg•°C: 0.244, 0.243, 0.242. Saturated vapor pressure of water, in kcal/cm² (absolute): 0.483, 0.1258, 0.0433. 7. The materials entering the hydrogen system (based on 1000 kg of 100% NaOH as a reference): Hydrogen: 12.5 kmol (25 kg); Water vapor: 11.39 kmol (205 kg); Other gases: × = 0.255 kmol (7.39 kg). Other impurities are not considered. III. Process Calculations (I) Single-stage Washing Cooling Tower 1. Calculation Basis: The temperature of hydrogen in the single-stage cooling tower decreases from 80°C to 50°C; the calculation is based on the production of hydrogen from 1000 kg of 100% NaOH. 2. Material Balance: ⑴ Let WL be the amount of water condensed in the hydrogen. Using Dalton’s law of partial pressures, an equation is established: = Solving this equation gives WL1 = 172 (kg). Since the solubility of gases in water is very low, this value is ignored. Then the composition of the gas exiting the tower is as follows: Hydrogen: 12.5 kmol (25 kg); Water vapor: 1.833 kmol (205 – 172 = 33 kg); Other gases: 0.255 kmol (7.39 kg).
(2) Material balance table
a. Using 1000 kg of 100% NaOH for hydrogen production as the calculation basis
Table 2-2: Material balance table for the first washing and cooling tower
| Name | Inflow to first washing and cooling tower (kg) | Outflow from first washing and cooling tower (kg) |
|------|---------------------------------------------------|---------------------------------------------------|
| Hydrogen | 25 | 25 |
| Water vapor | 205 | 33 |
| Other gases | 7.39 | 7.39 |
| Water | 172 | |
| Total | 237.39 | 237.39 |
b. Overall material balance
Table 2-3: Overall material balance table for the first washing and cooling tower
| Name | Inflow to first washing and cooling tower (kg) | Outflow from first washing and cooling tower (kg) |
|------|---------------------------------------------------|---------------------------------------------------|
| Hydrogen | 5,000,000 | 5,000,000 |
| Water vapor | 41,000,000 | 6,600,000 |
| Other gases | 1,478,000 | 1,478,000 |
| Water | 34,400,000 | |
| Total | 47,478,000 | 47,478,000 |
3. Heat balance
(1) Heat brought in by the gas entering the tower:
Q1 = 80 × 25 × 3.439 = 6,878 kcal
Q2 = 205 × 631.4 = 129,437 kcal
Q3 = 80 × 0.244 × 7.39 = 144 kcal
(2) Heat taken away by the cooling water:
Assuming the volume of cooling water is WL2 kg, with a temperature of 25°C; the temperature of the water exiting the tower is 50°C. Then the volume of water exiting the tower is WL2 + 172.
Heat brought in by the cooling water: Q4 = WL2 × 25
Heat taken away by the cooling water: Q5 = (WL2 + 172) × 50
(3) Heat taken away by the gas exiting the tower:
Q6 = 50 × 25 × 3.421 = 4,276 kcal
Q7 = 33 × 619.1 = 20,430 kcal
Q8 = 50 × 7.39 × 0.243 = 90 kcal
(4) Ignoring heat losses:
Q_in = Q_out
Therefore, Q1 + Q2 + Q3 + Q4 = Q5 + Q6 + Q7 + Q8
6,878 + 129,437 + 144 + 25 × WL2 = (WL2 + 172) × 50 + 4,276 + 20,430 + 90
Thus, WL2 = 4,122.52 kg
That is, the amount of water entering the system is 4,122.52 kg, while the amount of water exiting the system is 4,122.52 + 172 = 4,294.52 kg.
Heat brought in by the cooling water: 4,122.52 × 25 = 103,063 kcal
Heat taken away by the cooling water: (4,122.52 + 172) × 50 = 214,726 kcal
(5) Heat balance table
Table 2-4: Heat balance table for the first washing and cooling tower
| Input/Output | Material name | Quantity (kg) | Heat (kcal) |
|---------------|---------------|----------------|--------------|
| Input | Hydrogen | 25 | 6,878 |
| | Water vapor | 205 | 129,437 |
| Output | Hydrogen | 25 | 4,276 |
| | Water vapor | 33 | 20,430 |
| | Other gases | 7.39 | 144 |
| | Other gases | 7.39 | 90 |
| Input | Cooling water | 4,122.52 | 103,063 |
| Output | Cooling water | 4,294.52 | 214,726 |
| Total | | | 239,522 |
| | | | 43,599.1 |
(II) Second washing and cooling tower
1. Calculation basis
(1) The temperature of the electrolyzed hydrogen is reduced from 50°C to 30°C through two stages of washing and cooling. ⑵ Hydrogen purity: 98%
2. Material balance
(1) The temperature at the outlet of hydrogen from the two-stage scrubbing and cooling tower is 30°C; thus, the amount of condensed water is WL3. Similarly, using Dalton’s law of partial pressures, we can set up an equation: = Solving this yields WL3 = 22.61 kg. Therefore, the composition of the gas exiting the tower is as follows:
Hydrogen: 12.5 kmol (25 kg)
Water vapor: 0.577 kmol (33 – 22.61 = 10.39 kg)
Other gases: 0.255 kmol (7.39 kg)
(2) The proportion of hydrogen in the gas exiting the tower is 93.76%; the percentage of hydrogen in dry gas is 98%.
(3) Material balance table
a. Using 1000 kg of 100% NaOH as the basis for calculation:
Table 2-5: Material balance table for the two-stage scrubbing and cooling tower
| Substance | Input to tower (kg) | Output from tower (kg) |
|-----------|-------------------|----------------------|
| Hydrogen | 25 | 25 |
| Water vapor | 33 | 10.39 |
| Other gases | 7.39 | 7.39 |
| Water | 22.61 | — |
| Total | 65.39 | 65.39 |
b. Overall material balance:
Table 2-6: Overall material balance table for the two-stage scrubbing and cooling tower
| Substance | Input to tower (kg) | Output from tower (kg) |
|-----------|-------------------|----------------------|
| Hydrogen | 5,000,000 | 5,000,000 |
| Water vapor | 6,600,000 | 2,078,000 |
| Other gases | 1,478,000 | 1,478,000 |
| Water | 4,522,000 | — |
| Total | 13,078,000 | 13,078,000 |
3. Heat balance
(1) Heat carried away by gases:
Q6 = 4,276 kcal; Q7 = 20,433 kcal; Q8 = 90 kcal
(2) Heat carried away by gases:
Q9 = 30 × 25 × 3.049 = 2,557 kcal;
Q10 = 10.39 × 610.6 = 6,344 kcal;
Q11 = 30 × 7.39 × 0.242 = 54 kcal
(3) Heat carried away by cooling water:
Let WL4 be the mass of cooling water entering the system; its temperature is 25°C, while the temperature at the tower outlet is 30°C. Thus, the total mass of water exiting the tower is WL4 + WL2 = WL4 + 22.61 kg.
Heat brought in by incoming water: Q13 = WL4 × 25
Heat carried away by outgoing water: Q12 = (WL4 + 22.61) × 30
(4) Ignoring heat losses, we have:
Q_in = Q_out
Thus:
2,557 + 6,344 + 54 + (WL4 + 22.61) × 30 = 4,276 + 20,430 + 90 + WL4 × 25
Solving this gives WL4 = 3,032.54 kg. Therefore, the mass of cooling water entering the tower is 3,032.54 kg, while the mass exiting the tower is 3,032.54 + 22.61 = 3,055.15 kg.
Heat brought in by incoming water: 3,032.54 × 25 = 75,813.5 kcal
Heat carried away by outgoing water: (3,032.54 + 22.61) × 30 = 91,654.5 kcal
(5) Heat balance table:
Table 2-7: Heat balance table for the two-stage scrubbing and cooling tower
| Input | Output |
|-------|--------|
| Substance | Quantity (kg) | Heat (kcal) | Substance | Quantity (kg) | Heat (kcal) |
| Hydrogen | 25 | 6,878 | Hydrogen | 2.5 | 4,276 |
| Water vapor | 33 | 129,437 | Water vapor | 33 | 20,430 |
| Other gases | 7.39 | 144 | Other gases | 7.39 | 90 |
| Cooling water | 4,122.52 | 103,063 | Cooling water | 4,294.52 | 214,726 |
| Total | 4,337.41 | 239,522 | Total | 4,337.41 | 239,522 |
Chapter 3: Design and selection of main equipment
I. Single-stage scrubbing tower
1. Gas flow rate through the tower:
The temperature of gas entering the tower is 80°C, with operating pressure at 1 atmosphere. The total number of moles of gas is:
(12.5 + 11.39 + 0.255) × 26.52 = 640.33 kmol/h
Hence, the volume of gas is:
V = 22.4 × 640.33 × 1 = 18,546.58 m³/h
The total number of moles of gas exiting the tower is:
(12.5 + 1.833 + 0.255) × 26.52 = 386.87 kmol/h
Thus, the volume of gas exiting the tower is:
V = 22.4 × 38876 × 1 = 10,253.05 m³/h
The average gas volume is:
V_avg = 14,399.82 m³/h
2. Diameter of the tower:
Assuming an empty-tower velocity of 0.3 m/s, the diameter D is calculated as:
D = 4.12 m
Therefore, the tower diameter is taken as 4.2 m.
3. Determination and arrangement of nozzles for brine delivery:
Assuming the water supply pressure is 0.2 MPa, and considering possible clogging due to scale formation, the nozzle diameter is set at 3.5 mm. Based on tables, the water flow rate per nozzle is approximately 360 kg/h. Given that 109.33 tons/hour of cooling water at 25°C is required, the total number of nozzles needed is:
n = 303.69
To account for potential clogging issues, 400 nozzles are used instead. 4. Determination of tower height: The nozzles are arranged in 7 layers. There are 50 nozzles facing upward in the lower layer, 35 nozzles facing downward in the upper layer. In the middle 5 layers, there are 60 nozzles per layer, arranged offset from those in the upper and lower layers, spraying water downward. The spacing between pipes is 800 mm; this value increases to 1000 mm in the upper part due to the need for a degassing chamber, and to 2000 mm in the lower part due to the presence of air inlets. Thus, the total tower height is: H = 1000 + 2000 + 7 × 800 = 8600 mm.
5. Selection of pipe diameter: The gas flow velocity inside the pipes is set at 5 m/s. The flow rate of gas entering the tower is 18546.58 m³/h, which equals 5.15 m³/h. Therefore, the diameter of the pipe for gas entering the tower, d1, is 1200 mm. Similarly, the diameter of the pipe for gas leaving the tower is calculated as follows: The flow rate of gas leaving the tower is 10253.05 m³/h, or 2.85 m³/s. Hence, d2 = 0.85 m, or 850 mm. For the cooling water inlet, with a flow velocity of 2 m/s, the diameter d3 is calculated to be 0.139 m; it is chosen to be 150 mm.
II. Two-stage washing tower
1. Gas flow rate through the tower: V = 10253.05 m³/h. The volume of gas leaving the tower is… The temperature of the gas leaving the tower is 30°C, and the operating pressure is approximately 1 atmosphere. Therefore, the total molar amount of gas leaving the tower is: (12.5 + 0.577 + 0.255) × 26.52 = 353.565 kmol/h. V2 = 22.4 × 353.565 × 1 = 8790.17; this value further becomes 9521.61.
2. Determination of tower diameter: Using actual production data, the empty-tower velocity is set at 0.3 m/s. Thus, D = 3.35 m, and the tower diameter is chosen to be 3500 mm.
3. Number of nozzles: Assuming the water supply pressure is 0.2 Mpa, and considering potential blockage by scale, the nozzle diameter is set at 2.5 mm. Based on tables, the water spray rate is 280 kg/h. Using mass balance calculations, the required number of nozzles is 299.04. Considering distribution issues and possible blockages, 350 nozzles are selected.
4. Determination of tower height: The nozzles are arranged in 7 layers. There are 30 nozzles facing downward in the upper layer, 55 nozzles per layer in the middle 5 layers, arranged offset from those in the upper and lower layers, spraying water downward. There are 45 nozzles facing upward in the lower layer. The spacing between pipes is 800 mm; this value increases to 1000 mm in the upper part due to the need for a degassing chamber, and to 2000 mm in the lower part due to the presence of air inlets. Thus, the total tower height is: H = 1000 + 2000 + 7 × 800 = 8600 mm.
5. Selection of pipe diameters: The diameter of the pipe for gas entering the tower, d1, and d2, is 850 mm. The diameter of the pipe for gas leaving the tower is 0.789 m; it is chosen to be 800 mm. For the cooling water inlet, with a flow velocity of 2 m/s, the diameter d6 is calculated to be 0.122 m; it is chosen to be 130 mm.
III. Calculation of main pipe diameters
1. Diameter of the hydrogen gas pipe entering the system: D1 = d1 = 1200 mm.
2. Diameter of the hydrogen gas pipe after compression: With a flow velocity of 12 m/s, D2 = 0.509 m; rounded up to 530 mm.
3. Diameter of the pipe for water at 25°C entering the system: D3 = 0.185 m; rounded up to 200 mm.
4. Diameter of the pipe for cooling water leaving the system: D4 = 0.817 m; rounded up to 200 mm.
IV. Hydrogen delivery equipment: Since the hourly hydrogen delivery volume is 8790.17 m³/h, or 146.5 m³/min, and assuming an efficiency of 80%, the capacity of the hydrogen delivery equipment should be 183.13 m³/min. If three units are used in parallel with an efficiency of 60% each, then each unit’s capacity would be 101.74 m³/min. Four TR series two-stage Roots blowers are selected, with a flow range of 2.61–207 m³/min and a pressure increase of 9.8–196 Kpa.
V. Water delivery pumps: The water flow rate from the circulation tank is (113.89 + 84.33) = 198.22 m³/h. Assuming a head loss and resistance of 20 m (actual values depend on the actual pipeline resistance), according to the “Chemical Process Design Handbook” P1-72, the parameters for the 150F-35 type corrosion-resistant centrifugal pump are as follows: Flow rate: 234 m³/h, Head: 29.7 m, Motor power: 30 KW, Shaft power: 25.2 KW. Since the hydrogen gas produced by electrolysis contains a certain amount of alkaline mist, which makes the circulating water alkaline after washing, two 150F-35 type pumps are selected, one in operation and one as a backup. VI. Liquid-seal circulation tank: According to the design specifications, the distance between the first and second stage scrubbers is 1.5 m, while the distance between the surrounding walls is 0.8 m. Therefore, the length of the liquid-seal circulation tank is: 0.8×2 + 3.6 + 3.0 + 1.5 = 9.7 m, which is rounded up to 10 m. Thus, the distance between the scrubbers should be increased from 1.5 m to 1.8 m. The width is 0.8×2 + 3.6 = 5.2 m. The depth, which is also the height, is determined based on the water volume required for half an hour; hence, H = 1.91 m, rounded up to 2 m. The dimensions of the circulation tank are therefore 10,000 × 5,200 × 2,000.
VII. Hydrogen buffer tank: Based on the volume of gas exiting the scrubbers, the volume V = 2.44 m³/s. After rounding, the dimensions of the equipment are Φ1500×1900.
List of main equipment:
| Serial No. | Equipment Location | Equipment Name | Specifications | Quantity | Unit |
| 1 | E-1001 | Titanium cooler | Φ700×10,000 | 2 | units |
| 2 | V-1003 | Demister | Φ700×900 | 2 | units |
| 3 | T-1001 | Sulfuric acid drying tower I | Dg=1200 | 1 | unit |
| 4 | T-1002 | Sulfuric acid drying tower II | Dg=900 | 1 | unit |
| 5 | T-101-1 | First-stage scrubber | Dg=4,200 | 1 | unit |
| 6 | T-101-2 | Second-stage scrubber | Dg=3,500 | 1 | unit |
| 7 | P-101 | Circulation water pump | 150F-35 | 2 | units |
| 8 | C-101 | Roots blower, TR type | – | 4 | units |
| 9 | V-101 | Hydrogen buffer tank | Φ1500×1900 | 1 | unit |
(2) Material balance table
a. Using 1000 kg of 100% NaOH for hydrogen production as the calculation basis
Table 2-2: Material balance table for the first washing and cooling tower
| Name | Inflow to first washing and cooling tower (kg) | Outflow from first washing and cooling tower (kg) |
|------|---------------------------------------------------|---------------------------------------------------|
| Hydrogen | 25 | 25 |
| Water vapor | 205 | 33 |
| Other gases | 7.39 | 7.39 |
| Water | 172 | |
| Total | 237.39 | 237.39 |
b. Overall material balance
Table 2-3: Overall material balance table for the first washing and cooling tower
| Name | Inflow to first washing and cooling tower (kg) | Outflow from first washing and cooling tower (kg) |
|------|---------------------------------------------------|---------------------------------------------------|
| Hydrogen | 5,000,000 | 5,000,000 |
| Water vapor | 41,000,000 | 6,600,000 |
| Other gases | 1,478,000 | 1,478,000 |
| Water | 34,400,000 | |
| Total | 47,478,000 | 47,478,000 |
3. Heat balance
(1) Heat brought in by the gas entering the tower:
Q1 = 80 × 25 × 3.439 = 6,878 kcal
Q2 = 205 × 631.4 = 129,437 kcal
Q3 = 80 × 0.244 × 7.39 = 144 kcal
(2) Heat taken away by the cooling water:
Assuming the volume of cooling water is WL2 kg, with a temperature of 25°C; the temperature of the water exiting the tower is 50°C. Then the volume of water exiting the tower is WL2 + 172.
Heat brought in by the cooling water: Q4 = WL2 × 25
Heat taken away by the cooling water: Q5 = (WL2 + 172) × 50
(3) Heat taken away by the gas exiting the tower:
Q6 = 50 × 25 × 3.421 = 4,276 kcal
Q7 = 33 × 619.1 = 20,430 kcal
Q8 = 50 × 7.39 × 0.243 = 90 kcal
(4) Ignoring heat losses:
Q_in = Q_out
Therefore, Q1 + Q2 + Q3 + Q4 = Q5 + Q6 + Q7 + Q8
6,878 + 129,437 + 144 + 25 × WL2 = (WL2 + 172) × 50 + 4,276 + 20,430 + 90
Thus, WL2 = 4,122.52 kg
That is, the amount of water entering the system is 4,122.52 kg, while the amount of water exiting the system is 4,122.52 + 172 = 4,294.52 kg.
Heat brought in by the cooling water: 4,122.52 × 25 = 103,063 kcal
Heat taken away by the cooling water: (4,122.52 + 172) × 50 = 214,726 kcal
(5) Heat balance table
Table 2-4: Heat balance table for the first washing and cooling tower
| Input/Output | Material name | Quantity (kg) | Heat (kcal) |
|---------------|---------------|----------------|--------------|
| Input | Hydrogen | 25 | 6,878 |
| | Water vapor | 205 | 129,437 |
| Output | Hydrogen | 25 | 4,276 |
| | Water vapor | 33 | 20,430 |
| | Other gases | 7.39 | 144 |
| | Other gases | 7.39 | 90 |
| Input | Cooling water | 4,122.52 | 103,063 |
| Output | Cooling water | 4,294.52 | 214,726 |
| Total | | | 239,522 |
| | | | 43,599.1 |
(II) Second washing and cooling tower
1. Calculation basis
(1) The temperature of the electrolyzed hydrogen is reduced from 50°C to 30°C through two stages of washing and cooling. ⑵ Hydrogen purity: 98%
2. Material balance
(1) The temperature at the outlet of hydrogen from the two-stage scrubbing and cooling tower is 30°C; thus, the amount of condensed water is WL3. Similarly, using Dalton’s law of partial pressures, we can set up an equation: = Solving this yields WL3 = 22.61 kg. Therefore, the composition of the gas exiting the tower is as follows:
Hydrogen: 12.5 kmol (25 kg)
Water vapor: 0.577 kmol (33 – 22.61 = 10.39 kg)
Other gases: 0.255 kmol (7.39 kg)
(2) The proportion of hydrogen in the gas exiting the tower is 93.76%; the percentage of hydrogen in dry gas is 98%.
(3) Material balance table
a. Using 1000 kg of 100% NaOH as the basis for calculation:
Table 2-5: Material balance table for the two-stage scrubbing and cooling tower
| Substance | Input to tower (kg) | Output from tower (kg) |
|-----------|-------------------|----------------------|
| Hydrogen | 25 | 25 |
| Water vapor | 33 | 10.39 |
| Other gases | 7.39 | 7.39 |
| Water | 22.61 | — |
| Total | 65.39 | 65.39 |
b. Overall material balance:
Table 2-6: Overall material balance table for the two-stage scrubbing and cooling tower
| Substance | Input to tower (kg) | Output from tower (kg) |
|-----------|-------------------|----------------------|
| Hydrogen | 5,000,000 | 5,000,000 |
| Water vapor | 6,600,000 | 2,078,000 |
| Other gases | 1,478,000 | 1,478,000 |
| Water | 4,522,000 | — |
| Total | 13,078,000 | 13,078,000 |
3. Heat balance
(1) Heat carried away by gases:
Q6 = 4,276 kcal; Q7 = 20,433 kcal; Q8 = 90 kcal
(2) Heat carried away by gases:
Q9 = 30 × 25 × 3.049 = 2,557 kcal;
Q10 = 10.39 × 610.6 = 6,344 kcal;
Q11 = 30 × 7.39 × 0.242 = 54 kcal
(3) Heat carried away by cooling water:
Let WL4 be the mass of cooling water entering the system; its temperature is 25°C, while the temperature at the tower outlet is 30°C. Thus, the total mass of water exiting the tower is WL4 + WL2 = WL4 + 22.61 kg.
Heat brought in by incoming water: Q13 = WL4 × 25
Heat carried away by outgoing water: Q12 = (WL4 + 22.61) × 30
(4) Ignoring heat losses, we have:
Q_in = Q_out
Thus:
2,557 + 6,344 + 54 + (WL4 + 22.61) × 30 = 4,276 + 20,430 + 90 + WL4 × 25
Solving this gives WL4 = 3,032.54 kg. Therefore, the mass of cooling water entering the tower is 3,032.54 kg, while the mass exiting the tower is 3,032.54 + 22.61 = 3,055.15 kg.
Heat brought in by incoming water: 3,032.54 × 25 = 75,813.5 kcal
Heat carried away by outgoing water: (3,032.54 + 22.61) × 30 = 91,654.5 kcal
(5) Heat balance table:
Table 2-7: Heat balance table for the two-stage scrubbing and cooling tower
| Input | Output |
|-------|--------|
| Substance | Quantity (kg) | Heat (kcal) | Substance | Quantity (kg) | Heat (kcal) |
| Hydrogen | 25 | 6,878 | Hydrogen | 2.5 | 4,276 |
| Water vapor | 33 | 129,437 | Water vapor | 33 | 20,430 |
| Other gases | 7.39 | 144 | Other gases | 7.39 | 90 |
| Cooling water | 4,122.52 | 103,063 | Cooling water | 4,294.52 | 214,726 |
| Total | 4,337.41 | 239,522 | Total | 4,337.41 | 239,522 |
Chapter 3: Design and selection of main equipment
I. Single-stage scrubbing tower
1. Gas flow rate through the tower:
The temperature of gas entering the tower is 80°C, with operating pressure at 1 atmosphere. The total number of moles of gas is:
(12.5 + 11.39 + 0.255) × 26.52 = 640.33 kmol/h
Hence, the volume of gas is:
V = 22.4 × 640.33 × 1 = 18,546.58 m³/h
The total number of moles of gas exiting the tower is:
(12.5 + 1.833 + 0.255) × 26.52 = 386.87 kmol/h
Thus, the volume of gas exiting the tower is:
V = 22.4 × 38876 × 1 = 10,253.05 m³/h
The average gas volume is:
V_avg = 14,399.82 m³/h
2. Diameter of the tower:
Assuming an empty-tower velocity of 0.3 m/s, the diameter D is calculated as:
D = 4.12 m
Therefore, the tower diameter is taken as 4.2 m.
3. Determination and arrangement of nozzles for brine delivery:
Assuming the water supply pressure is 0.2 MPa, and considering possible clogging due to scale formation, the nozzle diameter is set at 3.5 mm. Based on tables, the water flow rate per nozzle is approximately 360 kg/h. Given that 109.33 tons/hour of cooling water at 25°C is required, the total number of nozzles needed is:
n = 303.69
To account for potential clogging issues, 400 nozzles are used instead. 4. Determination of tower height: The nozzles are arranged in 7 layers. There are 50 nozzles facing upward in the lower layer, 35 nozzles facing downward in the upper layer. In the middle 5 layers, there are 60 nozzles per layer, arranged offset from those in the upper and lower layers, spraying water downward. The spacing between pipes is 800 mm; this value increases to 1000 mm in the upper part due to the need for a degassing chamber, and to 2000 mm in the lower part due to the presence of air inlets. Thus, the total tower height is: H = 1000 + 2000 + 7 × 800 = 8600 mm.
5. Selection of pipe diameter: The gas flow velocity inside the pipes is set at 5 m/s. The flow rate of gas entering the tower is 18546.58 m³/h, which equals 5.15 m³/h. Therefore, the diameter of the pipe for gas entering the tower, d1, is 1200 mm. Similarly, the diameter of the pipe for gas leaving the tower is calculated as follows: The flow rate of gas leaving the tower is 10253.05 m³/h, or 2.85 m³/s. Hence, d2 = 0.85 m, or 850 mm. For the cooling water inlet, with a flow velocity of 2 m/s, the diameter d3 is calculated to be 0.139 m; it is chosen to be 150 mm.
II. Two-stage washing tower
1. Gas flow rate through the tower: V = 10253.05 m³/h. The volume of gas leaving the tower is… The temperature of the gas leaving the tower is 30°C, and the operating pressure is approximately 1 atmosphere. Therefore, the total molar amount of gas leaving the tower is: (12.5 + 0.577 + 0.255) × 26.52 = 353.565 kmol/h. V2 = 22.4 × 353.565 × 1 = 8790.17; this value further becomes 9521.61.
2. Determination of tower diameter: Using actual production data, the empty-tower velocity is set at 0.3 m/s. Thus, D = 3.35 m, and the tower diameter is chosen to be 3500 mm.
3. Number of nozzles: Assuming the water supply pressure is 0.2 Mpa, and considering potential blockage by scale, the nozzle diameter is set at 2.5 mm. Based on tables, the water spray rate is 280 kg/h. Using mass balance calculations, the required number of nozzles is 299.04. Considering distribution issues and possible blockages, 350 nozzles are selected.
4. Determination of tower height: The nozzles are arranged in 7 layers. There are 30 nozzles facing downward in the upper layer, 55 nozzles per layer in the middle 5 layers, arranged offset from those in the upper and lower layers, spraying water downward. There are 45 nozzles facing upward in the lower layer. The spacing between pipes is 800 mm; this value increases to 1000 mm in the upper part due to the need for a degassing chamber, and to 2000 mm in the lower part due to the presence of air inlets. Thus, the total tower height is: H = 1000 + 2000 + 7 × 800 = 8600 mm.
5. Selection of pipe diameters: The diameter of the pipe for gas entering the tower, d1, and d2, is 850 mm. The diameter of the pipe for gas leaving the tower is 0.789 m; it is chosen to be 800 mm. For the cooling water inlet, with a flow velocity of 2 m/s, the diameter d6 is calculated to be 0.122 m; it is chosen to be 130 mm.
III. Calculation of main pipe diameters
1. Diameter of the hydrogen gas pipe entering the system: D1 = d1 = 1200 mm.
2. Diameter of the hydrogen gas pipe after compression: With a flow velocity of 12 m/s, D2 = 0.509 m; rounded up to 530 mm.
3. Diameter of the pipe for water at 25°C entering the system: D3 = 0.185 m; rounded up to 200 mm.
4. Diameter of the pipe for cooling water leaving the system: D4 = 0.817 m; rounded up to 200 mm.
IV. Hydrogen delivery equipment: Since the hourly hydrogen delivery volume is 8790.17 m³/h, or 146.5 m³/min, and assuming an efficiency of 80%, the capacity of the hydrogen delivery equipment should be 183.13 m³/min. If three units are used in parallel with an efficiency of 60% each, then each unit’s capacity would be 101.74 m³/min. Four TR series two-stage Roots blowers are selected, with a flow range of 2.61–207 m³/min and a pressure increase of 9.8–196 Kpa.
V. Water delivery pumps: The water flow rate from the circulation tank is (113.89 + 84.33) = 198.22 m³/h. Assuming a head loss and resistance of 20 m (actual values depend on the actual pipeline resistance), according to the “Chemical Process Design Handbook” P1-72, the parameters for the 150F-35 type corrosion-resistant centrifugal pump are as follows: Flow rate: 234 m³/h, Head: 29.7 m, Motor power: 30 KW, Shaft power: 25.2 KW. Since the hydrogen gas produced by electrolysis contains a certain amount of alkaline mist, which makes the circulating water alkaline after washing, two 150F-35 type pumps are selected, one in operation and one as a backup. VI. Liquid-seal circulation tank: According to the design specifications, the distance between the first and second stage scrubbers is 1.5 m, while the distance between the surrounding walls is 0.8 m. Therefore, the length of the liquid-seal circulation tank is: 0.8×2 + 3.6 + 3.0 + 1.5 = 9.7 m, which is rounded up to 10 m. Thus, the distance between the scrubbers should be increased from 1.5 m to 1.8 m. The width is 0.8×2 + 3.6 = 5.2 m. The depth, which is also the height, is determined based on the water volume required for half an hour; hence, H = 1.91 m, rounded up to 2 m. The dimensions of the circulation tank are therefore 10,000 × 5,200 × 2,000.
VII. Hydrogen buffer tank: Based on the volume of gas exiting the scrubbers, the volume V = 2.44 m³/s. After rounding, the dimensions of the equipment are Φ1500×1900.
List of main equipment:
| Serial No. | Equipment Location | Equipment Name | Specifications | Quantity | Unit |
| 1 | E-1001 | Titanium cooler | Φ700×10,000 | 2 | units |
| 2 | V-1003 | Demister | Φ700×900 | 2 | units |
| 3 | T-1001 | Sulfuric acid drying tower I | Dg=1200 | 1 | unit |
| 4 | T-1002 | Sulfuric acid drying tower II | Dg=900 | 1 | unit |
| 5 | T-101-1 | First-stage scrubber | Dg=4,200 | 1 | unit |
| 6 | T-101-2 | Second-stage scrubber | Dg=3,500 | 1 | unit |
| 7 | P-101 | Circulation water pump | 150F-35 | 2 | units |
| 8 | C-101 | Roots blower, TR type | – | 4 | units |
| 9 | V-101 | Hydrogen buffer tank | Φ1500×1900 | 1 | unit |
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