System and method for regulating ammonia production of urea hydrolysis device using unit condensate

Abstract

The present invention discloses a system and method for regulating the ammonia production of a urea hydrolysis device using condensate from a unit, belonging to the technical field of flue gas treatment for thermal power units. The system includes a No. 2 low-pressure heater, a No. 1 low-pressure heater, a deaerator, a unit feedwater pump, a D gate valve, a condensate booster pump, a hydrolysis reactor, a condensate flow regulating valve, an A gate valve, a B gate valve, and a C gate valve. The present invention uses high-temperature condensate from the unit's condensate system as the heat source for the urea hydrolysis device, regulating the ammonia production of the hydrolysis device by adjusting the flow rate of the high-temperature condensate. The condensate after heat release flows back into the unit's condensate system. A urea hydrolysis device cooling system is also provided to rapidly cool the urea hydrolysis device by extracting low-temperature condensate from the unit's condensate system, thereby reducing the pressure of the hydrolysis device. The system of the present invention has a simple structure, efficiently utilizes heat transfer media and its heat, reduces waste of reducing agents, and avoids secondary pollution to the environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of flue gas treatment of thermal power units, and particularly relates to a system for regulating the ammonia production amount of a urea hydrolysis device by utilizing condensate of the unit and a control method thereof. Background Art

[0002] The main reducing agents for SCR flue gas denitrification are liquid ammonia, urea, and aqueous ammonia. Liquid ammonia is a hazardous chemical, volatile, flammable, and explosive, and its transportation and use are strictly regulated. Urea is a neutral solid fertilizer with the highest nitrogen content. It is relatively stable, poses no direct environmental risk, and is easy to store and transport. Ammonia aqueous solution is safer than urea and liquid ammonia, but its low concentration, bulk, and high transportation costs and energy consumption for evaporation and gasification are significant. With increasing safety requirements in the power industry, urea has become the preferred reducing agent for SCR flue gas denitrification at thermal power plants. Urea as a reducing agent can be produced primarily through thermal decomposition and hydrolysis. Considering both investment and operating costs, most thermal power plants prefer the urea hydrolysis process, in which a urea solution is heated to 130-160°C and a pressure of 0.4-0.6 MPa to react and produce ammonia and carbon dioxide.

[0003] Currently, ammonia production in hydrolysis units is generally controlled by regulating the flow rate of saturated steam used to heat the urea solution. This saturated steam is typically drawn from the plant's auxiliary steam system and obtained after temperature and pressure reduction. Saturated steam at a pressure of 0.7-0.9 MPa releases latent heat through the steam coils in the hydrolysis unit, condensing to form hydrochloric acid, which is collected in an open drain tank. The temperature of the hydrochloric acid in the tank is around 90°C, and some of it can be used to dissolve urea. This results in low water utilization and heat efficiency. Furthermore, the hydrolysis unit itself has a large heat storage capacity. If the ammonia production from the spontaneous reaction in the urea hydrolysis unit exceeds the ammonia demand of the unit's SCR reactor, the accumulation of this steam over a long period of time will inevitably lead to overpressure in the hydrolysis unit's product gas. Directly discharging this steam to relieve the pressure would result in wasteful reducing agents and secondary pollution.

[0004] In the prior art, a Chinese patent with publication number CN 104192862 A discloses a method and device for producing ammonia by urea hydrolysis using boiler gas. The method utilizes boiler flue gas to heat the urea solution once in the flue, draws hot primary air into the urea hydrolysis device to heat the urea solution again to promote urea hydrolysis to produce an ammonia-containing mixed gas, and the hot primary air after heat release enters the SCR denitrification device to avoid heat loss in the heating medium. This technology achieves changes in the amount of ammonia produced by the hydrolysis device by adjusting the amount of hot primary air, but does not propose corresponding solutions to the excessive amount of ammonia produced by the spontaneous reaction of the hydrolysis device. In addition, due to the small specific heat capacity and low convective heat transfer coefficient of the gas, the heat exchange area of the hydrolysis device is extremely large, and the system investment is relatively high. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art and to provide a rationally designed system and control method for regulating the ammonia production of a urea hydrolysis device by utilizing condensate from the unit.

[0006] The technical solution adopted by the present invention to solve the above-mentioned problem is: a system for regulating the ammonia production amount of a urea hydrolysis device by using the condensate of the unit, characterized in that it includes a No. 2 low-pressure heater, a No. 1 low-pressure heater, a deaerator, a unit feed water pump, a D gate valve, a condensate booster pump, a hydrolysis reactor, a condensate flow regulating valve, an A gate valve, a B gate valve and a C gate valve; the outlet of the No. 2 low-pressure heater is connected to the inlet of the No. 1 low-pressure heater, the outlet of the No. 1 low-pressure heater is connected to the inlet of the deaerator, the outlet of the deaerator is connected to the inlet of the unit feed water pump, the outlet of the deaerator is connected to the inlet of the hydrolysis reactor through the D gate valve and the condensate booster pump, the outlet of the hydrolysis reactor is connected to the inlet of the deaerator through the condensate flow regulating valve and the C gate valve, the outlet of the No. 2 low-pressure heater is connected to the inlet of the hydrolysis reactor through the A gate valve and the condensate booster pump, and the outlet of the hydrolysis reactor is connected to the inlet of the No. 1 low-pressure heater through the condensate flow regulating valve and the B gate valve.

[0007] Furthermore, the outlet condensate temperature of the deaerator is 150-200°C.

[0008] Furthermore, the outlet condensate temperature of the No. 2 low-pressure heater is 100~130°C.

[0009] Furthermore, the hydrolysis reactor is provided with a temperature monitor and a pressure monitor.

[0010] A control method for regulating the ammonia production amount of a urea hydrolysis device using unit condensate includes the following steps:

[0011] Step 1: Close gate valves A and B, open gate valves C and D, start the condensate booster pump, heat the reaction solution in the hydrolysis reactor with high-temperature condensate, and return the condensate after heat release to the condensate system of the unit; increase the opening of the condensate flow regulating valve, the ammonia production of the hydrolysis reactor increases, and the pressure increases; reduce the opening of the condensate flow regulating valve, the ammonia production of the hydrolysis reactor decreases, and the pressure decreases; by adjusting the condensate flow, the ammonia production of the hydrolysis reactor is matched with the ammonia demand of the unit SCR reactor, and the operating pressure of the hydrolysis reactor is stabilized within the normal range.

[0012] Step 2: When the operating pressure of the hydrolysis reactor is higher than the set high alarm value, close gate valves A, B, C and D, stop the condensate booster pump, use the hydrolysis reactor's own heat storage to carry out the hydrolysis reaction, and gradually reduce the operating pressure of the hydrolysis reactor by supplying ammonia to the unit's SCR reactor.

[0013] Step 3: When the operating pressure of the hydrolysis reactor is higher than the set high alarm value, close the C valve and the D valve, open the A valve and the B valve, start the condensate booster pump, and use the low-temperature condensate to absorb heat from the reaction solution in the hydrolysis reactor. Increase the opening of the condensate flow regulating valve, and the temperature of the reaction solution in the hydrolysis reactor will drop rapidly, the hydrolysis reaction rate will decrease, the amount of ammonia produced will decrease, the pressure will decrease, and the condensate after absorbing heat will flow back to the condensate system of the unit.

[0014] Furthermore, in step 1, the normal operating pressure range of the hydrolysis reactor is 0.55±0.15 MPa.

[0015] Furthermore, in step 2, the operating pressure of the hydrolysis reactor is set to a high alarm value of 0.7 MPa.

[0016] Furthermore, in step three, the operating pressure of the hydrolysis reactor is set to a high alarm value of 0.8 MPa.

[0017] Compared with the existing technology, the present invention has the following advantages and effects: High-temperature condensate from the unit's condensate system is used as the heat source for the urea hydrolysis unit, and the flow rate of the high-temperature condensate is used to regulate the ammonia production of the hydrolysis unit. The condensate, after releasing heat, is returned to the unit's condensate system, heating the urea hydrolysis reaction process without wasting heat transfer fluid and its heat, thus achieving efficient utilization of the condensate and its heat. Furthermore, a urea hydrolysis unit cooling system is provided to rapidly cool the urea hydrolysis unit by extracting low-temperature condensate from the unit's condensate system, slowing the hydrolysis reaction rate and accelerating the balance between the ammonia production of the urea hydrolysis unit and the ammonia demand of the unit's SCR denitrification reactor. This avoids direct discharge and pressure relief of the hydrolysis unit's product gas or reaction solution, which would otherwise waste reducing agents and cause secondary pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the system structure of the present invention.

[0019] In the figure: No. 2 low-pressure heater 1, No. 1 low-pressure heater 2, deaerator 3, unit feed water pump 4, D gate valve 5, condensate booster pump 6, hydrolysis reactor 7, condensate flow regulating valve 8, A gate valve 9, B gate valve 10, C gate valve 11. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and through examples. The following examples are intended to explain the present invention but the present invention is not limited to the following examples.

[0021] Example

[0022] See also Figure 1In this embodiment, a system for regulating the ammonia production of a urea hydrolysis device using condensate from a unit includes a No. 2 low-pressure heater 1, a No. 1 low-pressure heater 2, a deaerator 3, a unit feed water pump 4, a D gate valve 5, a condensate booster pump 6, a hydrolysis reactor 7, a condensate flow regulating valve 8, an A gate valve 9, a B gate valve 10, and a C gate valve 11; the outlet of the No. 2 low-pressure heater 1 is connected to the inlet of the No. 1 low-pressure heater 2, the outlet of the No. 1 low-pressure heater 2 is connected to the inlet of the deaerator 3, and the outlet of the deaerator 3 is connected to the inlet of the unit feed water pump 4. The outlet of the deaerator 3 is connected to the inlet of the hydrolysis reactor 7 through the D gate valve 5 and the condensate booster pump 6, and the outlet of the hydrolysis reactor 7 is connected to the inlet of the deaerator 3 through the condensate flow regulating valve 8 and the C gate valve 11. The outlet of the No. 2 low-pressure heater 1 is connected to the inlet of the hydrolysis reactor 7 through the A gate valve 9 and the condensate booster pump 6, and the outlet of the hydrolysis reactor 7 is connected to the inlet of the No. 1 low-pressure heater 2 through the condensate flow regulating valve 8 and the B gate valve 10. The hydrolysis reactor 7 is provided with a temperature monitor and a pressure monitor.

[0023] A control method for regulating the ammonia production amount of a urea hydrolysis device using unit condensate includes the following steps:

[0024] Step 1: Close gate valve A 9 and gate valve B 10, open gate valve C 11 and gate valve D 5, start the condensate booster pump 6, heat the reaction solution in the hydrolysis reactor 7 with high-temperature condensate, and the condensate after heat release flows back to the condensate system of the unit; increase the opening of the condensate flow regulating valve 8, the ammonia production of the hydrolysis reactor 7 increases, and the pressure increases; reduce the opening of the condensate flow regulating valve 8, the ammonia production of the hydrolysis reactor 7 decreases, and the pressure decreases; by adjusting the condensate flow, the ammonia production of the hydrolysis reactor 7 is matched with the ammonia demand of the unit SCR reactor, and the operating pressure of the hydrolysis reactor 7 is stabilized within the normal range.

[0025] Step 2: When the operating pressure of the hydrolysis reactor 7 is higher than the set high alarm value, close the A gate valve 9, the B gate valve 10, the C gate valve 11 and the D gate valve 5, stop the condensate booster pump 6, use the self-storage heat of the hydrolysis reactor 7 to carry out the hydrolysis reaction, and gradually reduce the operating pressure of the hydrolysis reactor 7 by supplying ammonia to the SCR reactor of the unit.

[0026] Step 3: When the operating pressure of the hydrolysis reactor 7 is higher than the set high alarm value, close the C gate valve 11 and the D gate valve 5, open the A gate valve 9 and the B gate valve 10, start the condensate booster pump 6, and absorb heat from the reaction solution in the hydrolysis reactor 7 through the low-temperature condensate. The opening of the condensate flow regulating valve 8 is increased, the temperature of the reaction solution in the hydrolysis reactor 7 drops rapidly, the hydrolysis reaction rate decreases, the amount of ammonia produced decreases, the pressure decreases, and the condensate after absorbing heat flows back to the condensate system of the unit.

[0027] Combine Figure 1 The present invention is further described as follows:

[0028] A 350MW unit was operating at full load, and the SCR flue gas denitrification system required 145 kg / h of ammonia. The condensate temperature at the outlet of low-pressure heater 2 (No. 1), low-pressure heater 1 (No. 2), and deaerator 3 in the unit's condensate system was 152°C, 122°C, and 172°C. Under normal operating conditions, gate valves A 9 and B 10 were closed, gate valves C 11 and D 5 were opened, and condensate booster pump 6 was running. High-temperature condensate was pumped from the outlet of deaerator 3 to hydrolysis reactor 7 to heat the reaction solution. The condensate, after releasing heat at 162°C, was then returned to the inlet of deaerator 3 for reheating. During operation, the flow rate of high-temperature condensate pumped was 60 t / h, accounting for less than 1% of the unit's total condensate flow, and did not affect the normal operation of the unit's condensate system. The operating temperature of the hydrolysis reactor 7 is 150° C. and the operating pressure is 0.5 MPa, which are within the normal range. The ammonia production of the hydrolysis reactor 7 meets the ammonia consumption demand of the SCR denitrification reactor of the unit.

[0029] The 350MW unit rapidly decreased from full load to 230MW, significantly reducing ammonia demand for the SCR flue gas denitrification unit. The hydrolysis reactor pressure rose to 0.72 MPa, triggering a high alarm. Gate valves A and B remained closed, condensate booster pump 6 was shut down, and gate valves C and D were closed to maintain ammonia supply to the unit's SCR denitrification reactor. The hydrolysis reaction, utilizing the residual heat from the solution in hydrolysis reactor 7, gradually decreased ammonia production. The temperature and pressure of hydrolysis reactor 7 decreased. After the pressure dropped to 0.6 MPa, gate valves C and D were reopened, and the condensate booster pump 6 was restarted to resume ammonia supply.

[0030] The 350MW unit rapidly decreased from full load to 70MW, causing a sharp drop in ammonia demand from the SCR flue gas denitrification system. The pressure in hydrolysis reactor 7 quickly rose to 0.8 MPa, triggering a high-high alarm. Gate valve A 9 was opened, gate valve D 5 was closed, gate valve B 10 was opened, and gate valve C 11 was closed. The condensate booster pump 6 remained operational, maintaining ammonia supply to the unit's SCR denitrification reactor. Simultaneously, low-temperature condensate was used to cool and reduce the pressure of hydrolysis reactor 7. After absorbing heat, the condensate was returned to the unit's condensate system for reuse.

[0031] In this embodiment, high-temperature condensate from the unit's condensate system serves as the heat source for the urea hydrolysis unit. The flow rate of this high-temperature condensate regulates the ammonia production of the hydrolysis unit, and the released condensate flows back into the unit's condensate system. A urea hydrolysis unit cooling system is also implemented to rapidly cool the unit by extracting low-temperature condensate from the unit's condensate system, thereby reducing the pressure in the unit. This system features a simple structure, efficiently utilizes the heat transfer medium and its heat, reduces reducing agent waste, and avoids secondary pollution to the surrounding environment.

[0032] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0033] Although the present invention has been disclosed above with reference to the embodiments, it is not intended to limit the scope of protection of the present invention. Any changes and modifications made by any technician familiar with the technology without departing from the concept and scope of the present invention should fall within the scope of protection of the present invention.

Claims

1. A control method for regulating the ammonia production of a urea hydrolysis device using condensate from a unit, characterized in that: The system comprises a No. 2 low-pressure heater (1), a No. 1 low-pressure heater (2), a deaerator (3), a unit feed water pump (4), a D gate valve (5), a condensate booster pump (6), a hydrolysis reactor (7), a condensate flow regulating valve (8), an A gate valve (9), a B gate valve (10) and a C gate valve (11); the outlet of the No. 2 low-pressure heater (1) is connected to the inlet of the No. 1 low-pressure heater (2), the outlet of the No. 1 low-pressure heater (2) is connected to the inlet of the deaerator (3), and the outlet of the deaerator (3) is connected to the inlet of the unit feed water pump (4). The outlet of the deaerator (3) is connected to the inlet of the hydrolysis reactor (7) through the D gate valve (5) and the condensate booster pump (6), and the outlet of the hydrolysis reactor (7) is connected to the inlet of the deaerator (3) through the condensate flow regulating valve (8) and the C gate valve (11). The outlet of the No. 2 low-pressure heater (1) is connected to the inlet of the hydrolysis reactor (7) through the A gate valve (9) and the condensate booster pump (6), and the outlet of the hydrolysis reactor (7) is connected to the inlet of the No. 1 low-pressure heater (2) through the condensate flow regulating valve (8) and the B gate valve (10); The control method comprises the following steps: Step 1: Close gate valve A (9) and gate valve B (10), open gate valve C (11) and gate valve D (5), start the condensate booster pump (6), heat the reaction solution in the hydrolysis reactor (7) with high-temperature condensate, and return the condensate after heat release to the condensate system of the unit; increase the opening of the condensate flow regulating valve (8), increase the ammonia production of the hydrolysis reactor (7), and increase the pressure; reduce the opening of the condensate flow regulating valve (8), reduce the ammonia production of the hydrolysis reactor (7), and reduce the pressure; by adjusting the condensate flow, the ammonia production of the hydrolysis reactor (7) is matched with the ammonia demand of the unit SCR reactor, and the operating pressure of the hydrolysis reactor (7) is stabilized within the normal range; Step 2: When the operating pressure of the hydrolysis reactor (7) is higher than the set high alarm value, the gate valve A (9), the gate valve B (10), the gate valve C (11) and the gate valve D (5) are closed, the condensate booster pump (6) is stopped, and the hydrolysis reaction is carried out by utilizing the heat storage of the hydrolysis reactor (7) itself, and the operating pressure of the hydrolysis reactor (7) is gradually reduced by supplying ammonia to the SCR reactor of the unit; Step 3: When the operating pressure of the hydrolysis reactor (7) is higher than the set high alarm value, close the C gate valve (11) and the D gate valve (5), open the A gate valve (9) and the B gate valve (10), start the condensate booster pump (6), and absorb heat from the reaction solution in the hydrolysis reactor (7) through the low-temperature condensate. The opening of the condensate flow regulating valve (8) is increased, and the temperature of the reaction solution in the hydrolysis reactor (7) drops rapidly, the hydrolysis reaction rate decreases, the amount of ammonia produced decreases, the pressure decreases, and the condensate after absorbing heat flows back to the unit condensate system.

2. The control method for regulating the ammonia production amount of a urea hydrolysis device by utilizing condensate water of a unit according to claim 1, characterized in that: The outlet condensate temperature of the deaerator (3) is 150-200°C.

3. The control method for regulating the ammonia production amount of a urea hydrolysis device by utilizing condensate of a unit according to claim 1, characterized in that: The outlet condensate temperature of the No. 2 low-pressure heater (1) is 100-130°C.

4. The method for controlling the amount of ammonia produced by a urea hydrolysis device by utilizing condensate from a unit according to claim 1, characterized in that: The hydrolysis reactor (7) is provided with a temperature monitor and a pressure monitor.

5. The control method for regulating the ammonia production amount of a urea hydrolysis device by utilizing condensate of a unit according to claim 1, characterized in that: In step 1, the normal operating pressure range of the hydrolysis reactor (7) is 0.55±0.15 MPa.

6. The method for controlling the amount of ammonia produced by a urea hydrolysis device by utilizing condensate from a unit according to claim 1, characterized in that: In step 2, the operating pressure of the hydrolysis reactor (7) is set to a high alarm value of 0.7 MPa.

7. The method for controlling the amount of ammonia produced by a urea hydrolysis device by utilizing condensate from a unit according to claim 1, characterized in that: In step 3, the operating pressure of the hydrolysis reactor (7) is set to a high alarm value of 0.8 MPa.

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