Issues regarding heating with superheated steam and dry saturated steam

Such a theory is feasible. It is difficult to achieve this, and there are issues with power generation load balancing.

If the back pressure of the air separation turbine is high, the size of the unit has to increase significantly, which is not very suitable

Where do you think the specific problem lies? Could you specify it? If there is a problem with the balance, can it be adjusted using the pressure relief valve on the bypass line?

It seems like this doesn’t matter much; the parameters are already there, so it’s sufficient to just add a bypass with a different diameter in the main steam pipeline

Typical air compression units are of the condensing type, with an exhaust pressure of around 0.01 MPa(A). If you switch to a back-pressure type, the exhaust pressure becomes around 0.3 MPa. To maintain the shaft power, the volume of air intake must increase, which in turn means that the size of the equipment will have to increase as well; in such a case, manufacturers will not be able to produce the required equipment

The last edit to this post was made by arpcd on 2015-9-18 at 14:14. My straightforward opinion: Steam with a pressure of 15 t/h, which is medium-pressure superheated steam, becomes low-pressure superheated steam after passing through a pressure reducing valve; this process is an isenthalpic throttling process, meaning there is no heat loss. But now, since the steam is used for power generation, there is some heat loss. In essence, the lost heat (and power generation certainly requires heat) must be compensated for with additional medium-pressure superheated steam. . So the total consumption will definitely increase, but the actual thermal load of your equipment does not increase. The more power that is generated, the more heat is required, while the original steam consumption remains unchanged. It’s simpler to calculate using money: 15 tons of steam at 100 yuan per ton. The heat equipment consumes 1500 yuan worth of steam per hour, and this amount remains constant. Generating electricity also requires steam; for example, if 300 units of electricity are generated, at 0.6 yuan per unit, the selling price would be 180 yuan. Therefore, your costs should be somewhere between 120 and 150 yuan. . . . If electricity is being generated to be sold for money, shouldn’t you invest more steam as well? More steam consumption is certain. The numbers speak for themselves as well: (Note: All pressure values are in absolute terms; if gauge pressure is used, the user can perform the calculations themselves.) For superheated steam at 1.0 MPa and 240°C, the enthalpy value H1 is 2920.98 kJ/kg, while the flow rate is 15 t/h, which equals 15,000 kg/h. The total heat load Q is equal to W1 × H1, which amounts to 12170.75 kW. Since a pressure reducing valve operates in an isenthalpic process, it does not affect the total heat load – the only possible loss is due to minor heat losses. Therefore, whether the pressure is reduced to 0.3 MPa or 0.4 MPa, it has no impact on Q. The steam generated is superheated steam at 0.3 MPa and 150°C, with an enthalpy value of H2=2761.18 kJ/kg. The steam consumption amount W2 is calculated as Q/H2, which equals 12170.15*3600/2761.18 = 15868 kg/h, or 15.868 tons/h. Thus, the increase in steam consumption is 0.868 tons/h. From the perspective of material balance, at this point the system requires superheated steam at 1.0 MPa and 240°C; the consumption of such steam is W1’ = 15.868 t/h, while the total heat required is Q’ = 12875.11 kW. Compared to Q = 12170.75 kW, there is an additional amount of 12875.11 – 12170.75 = 704.36 kW. Assuming an efficiency of 65% for the back-pressure generator (it’s advisable to consult the manufacturer), the power generated is N = 704.36 * 0.65 = 457.83 kW. . Material balance: Input – 15.868 t/h of steam; Output – 15.868 t/h of condensed water. Balance~~~~~ Energy balance: Input – 12,875.11 kW; Output – 12,170.75 kW consumed by heat-using equipment + 457.83 kW generated + 246.53 kW lost during power generation = 12,875.11 kW. Balance~~~~~ Basic economic analysis: Assuming a power generation output of 400 kWh/h, and with a selling price of 400 x 0.6 = 240 yuan/h, the annual sales revenue for 8,000 hours per year is 240 * 0.8 = 1.92 million yuan. After deducting the cost of excess steam consumption, which is about 90 yuan/h (720,000 yuan per year), the net profit is around 1.2 million yuan. In other words, to recoup the costs within two years, the total cost of this additional small turbine and generator setup should be around 2.4 million yuan (including the total EPC cost for equipment procurement, installation, and commissioning). Profitability will begin after those two years. . Get along well: lol

The heat transfer coefficient of superheated steam is very low, requiring a much larger heat exchange area in the reboiler

Thank you, senior. Here’s the situation: Please take a look at this. There is 42 t/h of steam at 1.0 MPA after the air separation unit’s back pressure; this steam is used by customers, with approximately 6 tons being utilized. The remaining 24 t/h goes to the 0.3 MPA pipeline system via pressure reducers, while 12 t/h goes to the 0.6 MPA pipeline system through pressure reducers as well. The steam exiting the turbine is at 1.1 MPA and 315°C; after cooling it with water spray behind the turbine, its temperature drops to 220°C, and this steam is then used in the 10-kilogram pipeline system. When the steam volume decreases to 3 kilograms or 6 kilograms, no water spray is used for cooling – instead, superheated steam is used for heating. I think that the energy lost due to cooling and reducing the pressure of the steam behind the turbine is wasted; it would be better to use the steam at 315°C directly to drive two small turbines for power generation, with the steam at 6 kilograms and 3 kilograms being used by customers. Even if the steam consumption increases slightly, it doesn’t matter much, as there is already an excess of steam. The extra amount of superheated steam doesn’t result in a significant increase in total steam volume. I believe that our heat exchangers have sufficient heating surface area. Yet, the temperature in the 3-kilogram pipeline system still approaches 210°C, which seems like a waste. Perhaps it would be better to use two small turbines for this purpose. What do you think?

Since it is known that temperature reducers and pressure reducers result in a loss of exergy, you should calculate this using actual data. The following three posts contain practical calculations related to temperature reducers, pressure reducers, and turbine power generation; you can refer to them for more information: Do temperature reducers and pressure reducers in steam systems really waste energy? http://bbs.hcbbs.com/thread-1005020-1-1.html Is there any energy loss when superheated steam at 2.5MPa and 390℃ passes through a temperature and pressure reducing valve? http://bbs.hcbbs.com/thread-1009205-1-1.html Calculation of energy loss in temperature reduction regulators. http://bbs.hcbbs.com/thread-1390823-1-1.html As a technical engineer, you need to learn to do the calculations yourself; only by doing them personally can you truly understand the fundamental differences between temperature reduction regulators and back-pressure generators. You won’t be able to understand this without having the relevant data. I’m not sure either, hehe. . Calculate it by yourself; many technical professionals in companies have this problem – don’t just keep asking questions; you need to actually do the calculations yourself! ! Try it? ? ?

Senior, here’s the situation: there are still some issues. I’ve done some calculations as well. For example, take the use of a pressure reducing valve – parameters such as the inlet and outlet pressures of the control valve, the temperature of the superheated steam (T, in °C: 215 and 196), the pressure (P, in MPaG: 1.1 and 0.3), the flow rate (W, in kg/h: 24,000 and 24,000), specific enthalpy (H, in kJ/kg: 2,856.65 and 2,856.71), specific entropy (S, in kJ/kg·K: 6.7223 and 7.3391). The available energy (Ex, in kJ/kg) is 857.96 and 74.15 respectively. The total enthalpy is 18,991 kW for both cases, while the total available energy is 5,703 kW and 4,482–1,221 kW respectively. The loss of energy (Lw) is 1,221 kW in each case. It’s true that there is a loss of available energy, but I think what’s lost is actually a certain type of energy, namely exergy. There isn’t much difference in total energy; it’s just that the amount of available energy is greater in one case and less in the other. It can’t be said that there’s an energy loss after using a pressure reducing valve – rather, it’s the exergy that decreases, while the total energy remains unchanged. If we use either form of energy to generate electricity, they will definitely perform differently: one might be able to cover 100 meters while the other can only cover 50 meters. But if we use them for heating, both can achieve the same result, such as lifting something 100 meters high. If we don’t use them for generating electricity, then there isn’t much loss of energy. In the end, both end up as liquid, with a difference in enthalpy of 100 kJ/kg; the rest of the energy is used for heating. Now, if I use this steam to generate electricity, I need two or three more tons of steam for heating. At a cost of 160 yuan per ton, this results in additional costs of several hundred yuan. Moreover, the backpressure turbine also has its own efficiency. Using calculation software, assuming the inlet steam pressure is 1.0 MPa at 305 degrees Celsius, and the outlet steam pressure is 0.3 MPa at 222 degrees Celsius, with a flow rate of 24 T/h, and an efficiency of 0.65, the turbine can generate 1,016 kW of power. Similarly, at 0.6 MPa, it can drive power generation of 312 kW. Even when it comes to making money, it’s the difference between the cost of electricity and the amount saved by using steam more efficiently. At 65 cents per 1000 units of electricity, saving 650–320 yuan per hour means a savings of 330 yuan. Is this calculation correct? In that case, savings of several million yuan can be achieved in a year. There’s another issue: I’ve seen some factories use small steam turbines to drive small electric motors for power generation; it’s still a way of generating electricity, but I’m not sure what the efficiency is like. Is it worth using this method for power generation? Inlet pressure, inlet temperature, exhaust pressure, exhaust temperature, and the amount of work that can be done: 1.0 MPa, 305°C; 0.3 MPa, 222°C; 1016; 0.9 MPa, 305°C; 0.3 MPa, 229; 932; 0.8 MPa, 305°C; 0.3 MPa, 238; 837