Problems with the alkali pump in the first evaporation stage

We use the same ones as well; the first-stage pumps were imported, and later we used those produced by Jiangnan Chemical Equipment Factory, and their performance is quite good.

What is the material? Nickel 201?

The nickel pumps provided by Xi’an Pump and Valve Factory are very useful.

Yes, the material of the first-stage pump used in our factory is nickel 201! !

Reply to 1# renzongkai: We are supplied with the pumps for Stage 1 and Stage 2 directly by SET. But we haven’t finished installing it yet. Bro, give me some operational support.

The pumps provided by SET are made of nickel 201, but imported ones are too expensive and have a short lifespan as well. The impeller needs to be replaced every about 2 years. If you need help driving, you can turn to me.

Preface: Evaporation is an important unit operation in chemical production, and it is widely used in industries such as chemistry, food, and pharmaceuticals. In 1998 and 2000, our company introduced two sets of three-effect counter-current falling-film evaporation units from the Italian company SET for use in ion-exchange membrane electrolysis processes. The production capacity of each set is 360 t/d of 100% NaOH; the product specification is NaOH with a mass fraction of 50%, and the operating range is from 25% to 110% of the rated capacity. The equipment introduced in these two sets of systems includes first and second-effect evaporators, welded and gasketed plate heat exchangers, and pumps; the rest is domestically sourced. It has been in operation for over ten years now. I. Brief description of the process flow: The electrolyte produced by ion membrane electrolysis is pressurized by a liquid feeding pump (PU1305); after being measured by a flow meter (F0505), it enters the third-stage evaporator (HE1303) together with the recycled alkali from the third stage, where some of the water is removed through evaporation. The boiling alkali solution then enters the third-stage separation tank (D1303), where it is separated from the secondary steam. The separated alkali solution, along with that from the third-stage evaporator, is pumped out by the third-stage alkali pump (PU1303). Some of this solution is recycled and preheated in the first-stage preheater of the second stage (HE1308) and the second-stage preheater of the second stage (HE1307), before entering the second-stage evaporator (HE1302) together with the recycled alkali from the second stage, thereby further concentrating the alkali solution. The alkali solution from the second-stage separation tank (D1302), along with that from the second-stage evaporator, is pumped out by the second-stage alkali pump (PU1302). Some of this solution is recycled and preheated in the first-stage preheater of the first stage (HE1305) and the second-stage preheater of the first stage (HE1306), before entering the first-stage evaporator (HE1301) together with the recycled alkali from the first stage. There, the alkali solution is concentrated into finished alkali. The alkali solution from the first-stage separator (D1301) and that from the first-stage evaporator is pumped out by the first-stage alkali pump (PU1301). Some of this solution is recycled again, preheated in the first-stage preheater and the second-stage preheater, and finally cooled to a safe temperature in the finished alkali cooler (HE1309) before being fed into the finished alkali storage tank (S1302). Medium-pressure steam coming from outside the system passes through the pressure control system PIC0501 and the flow control system FIC0501, and after being humidified, enters the first-stage evaporator. The condensate is discharged into the vapor and water separation tank (D1305). The steam condensate exiting this tank passes through the second-stage preheater of the first stage and the second-stage preheater of the second stage before being sent to the steam condensate storage tank (S1304). The secondary steam from the first stage serves as a heat source for the second stage; after being humidified, it enters the second-stage evaporator, and the resulting condensate is discharged into the third-stage evaporator. The secondary steam from the second stage acts as a heat source for the third stage as well; after being humidified, it enters the third-stage evaporator, and the resulting condensate is discharged into the process condensate tank (D1304). The secondary steam generated in the third stage enters the surface condenser (HE1304) where it exchanges heat with circulating water; the condensate from there goes into the process condensate tank, while any uncondensed gas is removed by the vacuum pump (K1301) and discharged into the atmosphere, thereby maintaining a certain level of vacuum in the second and third stages. The condensate in the process condensate tank is pumped to the process condensate storage tank (S1303) using the process condensate transfer pump (PU1304). The process flow is as follows: • HE1301 – First-effect evaporator, HE1302 – Second-effect evaporator, HE1303 – Third-effect evaporator, HE1304 – Surface cooler; D1301 – First-effect separation tank, D1302 – Second-effect separation tank, D1303 – Third-effect separation tank, D1305 – Steam and water removal tank, D1304 – Process condensate tank; HE1305 – First-effect preheater stage 1, HE1308 – Second-effect preheater stage 1, HE1309 – Finished product cooler; D1304 – Process condensate tank; HE1306 – First-effect preheater stage 2, HE1307 – Second-effect preheater stage 2; K1301 – Vacuum pump; PU1301 – First-effect alkali pump, PU1302 – Second-effect alkali pump, PU1303 – Third-effect alkali pump. Table of main equipment materials: Equipment code, Equipment name, Material used, Remarks: 1. P-1301A/B – First-effect pumps, Ni200; 2. P-1302A/B – Second-effect pumps, Monel alloy; 3. P-1303A/B – Third-effect pumps, SUS316L; 4. D-1301A – First-effect evaporator separation tank, Ni200/Ni201 (Phase 1/Phase 2); 5. D-1302A – Second-effect evaporator separation tank, Ni200/Ni201 (Phase 1/Phase 2); 6. D-1303A – Third-effect evaporator separation tank, SUS316L; 7. E-1301A – First-effect evaporator, Ni201; 8. E-1302A – Second-effect evaporator, Ni201; 9. E-1303 – Third-effect evaporator, SUS316L. II. Process advantages: 1. Rational utilization of heat in this system. Thanks to the design that makes full use of the heat from the alkali in the first effect and the condensate from high-temperature steam, both the load on the finished product alkali cooler and the steam consumption of the system are reduced. The steam consumption for producing 45% liquid alkali is 0.46–0.47 t/t (100% NaOH), while it is 0.52–0.53 t/t (100% NaOH) for producing 50% liquid alkali. In addition, humidification is applied to the heat sources in each effect, thereby improving heat exchange efficiency. 2. Low alkali content in process condensate: The vapor-liquid separation tank in this system is highly efficient; based on more than 10 years of operational data, the alkali content in the process condensate remains below 10 ppm. The amount of alkali lost in this way is minimal, which creates favorable conditions for the recycling of the process condensate. 3. The vacuum system is stable and reliable. It is well known that the efficiency and reliability of the vacuum system in an evaporation unit directly determine the unit’s processing capacity, product quality, steam consumption, and the rate of equipment corrosion. I think the biggest advantage of this set is its vacuum system. It can stably ensure a vacuum level of over 90 Kpa for Stage III and over 60 Kpa for Stage II. Due to the strong ability of the vacuum pump to remove non-condensable gases, it effectively ensures the stable operation of the vacuum system; even minor leaks in the pipes do not affect it, making it more stable and reliable than hydraulic jet pumps. Water addition and vacuum breaking for leak detection are carried out once a year on the Class III and Class II separation tanks as well as the vacuum pipelines, which helps to ensure the efficient operation of the vacuum system. 4. The evaporators are properly protected. The medium-pressure steam coming from outside the system is first stabilized in pressure, and a safety valve is installed before it enters the first-stage evaporator; its set value is lower than the design pressure of the tube side of E1301. If the steam pressure becomes too high, this valve automatically releases the steam into the atmosphere, ensuring that the pressure of the steam entering the evaporator does not exceed safe levels. Safety valves are also installed on the steam inlet pipes of the second and third-stage evaporators, which helps to keep the operating pressure of these evaporators within specified limits and thus extends their service life. 5. Continuous non-condensable gas discharge pipelines are provided in each stage of the unit, effectively preventing the accumulation of non-condensable gas in the heating chamber and ensuring heat exchange efficiency. It is more reliable, more reasonable, and easier to manage than regular manual discharge. It fully demonstrates the sophistication of the design. 6. Precise control of alkali concentration: Thanks to the online density meter installed in this device, the alkali concentration of the product is effectively controlled, with the final product’s alkali concentration being easily maintained within ±0.2%. This not only ensures product quality and reduces consumption but also minimizes equipment corrosion. 7. Low labor intensity for workers and easy management: This set of evaporation units is controlled by DCS, resulting in low labor intensity for workers; one person is sufficient to carry out inspections at the site for these two sets of evaporation units. III. Existing deficiencies 1. Severe equipment corrosion: The high discharge temperature in Stage I (162°C, 50% liquid caustic) leads to severe corrosion of the equipment and pipelines. The average service life of the impeller in the first-effect pump is 2 years; the average service life of the HE1306 heat exchanger is 3 years, that of the HE1307 heat exchanger is 3.5 years, and those of the HE1305 and HE1308 heat exchangers is 5 years. The average service life of the third-effect evaporator is 8.5 years, while that of the first-effect evaporator is 9 years. The self-regulating valves that come into contact with alkalis have an even shorter lifespan, and they all need to be replaced after just over a year of operation of the plant. Leakages often occur in pipeline welds, which increases the workload for maintenance and leads to alkali loss. Furthermore, the production capacity of the unit is mostly affected by the capacity of the primary pump; a decrease in the capacity of this pump due to impeller corrosion impacts the overall capacity of the unit. Improving the operational adaptability of the primary pump is an aspect that needs to be addressed for this unit. 2. Complex piping configuration: Due to the presence of four heat exchangers, namely E1305, E1306, E1307, and E1308, the piping configuration is complex. This results in increased pipe length, more potential leakage points, and higher energy consumption. 3. Improper handling of substandard alkali in the early stages of operation: Since the density meter is located on the discharge pipeline, whether the concentration of the alkali produced in the first stage is high or low, it can only be sent to the tank for finished alkali, where it is then mixed to achieve the required standard. If there is an excessive amount of substandard alkali or the concentration deviates too much during the initial stages of operation, it becomes quite difficult to deal with this situation. To address this, we added an additional alkali outlet pipe leading to the electrolyte tank, which effectively solved the problem and also made it easier to start up the system in the absence of automatic level control. 4. There are no recovery devices at the points where pipes and pumps discharge their contents. Evaporation units are shut down for maintenance quite frequently, and before each maintenance session, a large amount of alkali is discharged from the pipes and equipment, which not only pollutes the environment but also leads to losses of alkali. Alkali recovery devices should be installed at the discharge and sampling points, which is in line with the principles of cleaner production and reduces alkali loss. IV. Conclusion: The three-effect counter-current falling-film evaporation unit introduced from the Italian company SET, after more than a decade of actual operation, has demonstrated advanced process technology, reliable operation, stable product quality, low energy consumption, and ease of production management. By appropriately improving the materials used for automatic control valves and the pumps in the first effect, as well as enhancing the quality of welding, it is possible to further reduce alkali loss and lower the steam consumption per unit of production. In summary, the three-effect counter-current falling-film evaporation unit from SET Company introduced by our factory is worth promoting.

We have imported nickel-free pumps that can solve this problem; you can add me on QQ at 185850176

Our factory also uses SET devices, but they haven’t been put into operation yet. We’re currently struggling to come up with the operating procedures. Could anyone give us some guidance? Thank you very much!

Give me your email and I’ll send it to you.