Continuous discharge expansion vessel and periodic discharge expansion vessel discharge recovery device (discharge cooler)
1、 Current situation analysis
During boiler operation, due to the limitations of water treatment conditions, the boiler feedwater always contains a certain amount of impurities. In order to ensure that the boiler water meets the prescribed standards (to ensure that the salt content of the boiler water is within the allowable range), it is necessary to discharge the boiler water There are two types of discharge methods: continuous discharge and periodic discharge
Continuous discharge refers to continuously discharging a portion of boiler water from the area near the evaporation surface of the steam drum with high salt concentration, and supplementing it with relatively clean feedwater to prevent excessive salt content in the boiler water and maintain a certain alkalinity of the boiler water
Regular discharge refers to the intermittent discharge of insoluble sediment and impurities such as rust that settle at the bottom of the boiler steam water
Boiler blowdown can control the salt content of boiler water, but it causes loss of working fluid and heat, so the amount of boiler blowdown should be limited. The amount of boiler blowdown is usually expressed by the blowdown rate P The pollution discharge rate is the percentage of the amount of pollution discharged to the boiler's evaporation capacity According to the "Regulations on Electric Power Technology Management (Trial)", the emission rate of condensing power plants is 1% to 2%, and the emission rate of thermal power plants is 2% to 5%
Continuous discharge from power plants is the main cause of loss of working fluid in power plants, and the amount of continuous discharge is almost equal to the total loss of other steam and water in the power plant In addition, due to the high temperature and pressure of wastewater discharge, it not only causes loss of working fluid and heat, but also pollutes the environment
In order to reduce the loss of working fluid and heat caused by sewage discharge, our company has launched a sewage cooling heat exchanger to recover and utilize sewage and steam. The main form of this recycling device is a surface cooler.
2、 Principle
The sewage cooler adopts a surface heat exchanger, which transfers the heat of the heated steam to the desalinated water (softened water) heated inside the tube bundle through a metal heating surface. The heat of the steam (part of which is introduced into the deaerator) and water (sewage) evaporated and separated after expansion of the fixed and continuous discharge containers is completely absorbed by the desalinated water (softened water), causing a significant increase in the temperature of the desalinated water and reducing the temperature of the sewage to below 50 ℃. It is discharged through the cooler's sewage outlet to the trench or drainage tank, achieving the function of recovering and utilizing the heat energy of the sewage.
The system process is as follows: the boiler discharge is connected to the continuous discharge expansion container and the periodic discharge expansion container, and the discharge water from the continuous discharge expansion container (connected to the steam separated by evaporation and the deaerator) is discharged into the periodic discharge expansion container. The steam and discharge water separated by evaporation in the periodic discharge expansion container enter the discharge cooler, and the discharge water is evaporated, separated and cooled again in the cooler. The remaining small amount of discharge water is cooled to below 50 ℃ and then discharged into the trench through the discharge outlet of the cooler. Please refer to the system diagram for details.
3、 Advantages:
1. The structure is simple and can be used for a long time without maintenance.
2. Good heat transfer effect and significant energy-saving effect.
3. Safe and reliable operation, with no adverse effects on the safe operation of the unit.
4. Eliminating air pollution and noise pollution caused by exhaust, optimizing the environment.
4、 Model number
PWL - 口 - 口
PWL stands for the first letter of the discharge cooler
口 represents cooling area
口 represents the volume of the discharge expansion container in m3
5、 Specific forms include: tubular and hybrid columns
There are vertical and horizontal types of pipes
The hybrid installation form is vertical
6、 Specification and model
Scope of application: Used in conjunction with regular sewage discharge expansion containers
|
Specification and model |
Drainage cooling area(㎡） |
Expansion container with limited area（㎡） |
Design pressure （MPa） |
Design Temperature （℃） |
operation temperature （℃） |
|
PWL-32-0.75 |
32 |
0.75 |
1.0 |
300 |
170 |
|
PWL-45-1.5 |
48 |
1.5 |
|||
|
PWL-60-3.5 |
60 |
3.5 |
|||
|
PWL-75-7.5 |
75 |
7.5 |
|||
|
PWL-100-12 |
100 |
12 |
6、 Production, manufacturing, and inspection standards
1. This equipment is designed, manufactured, and accepted in accordance with GB151-1999 "Shell and Tube Heat Exchanger" and "Technical Specification for Construction and Acceptance of Electric Power Construction".
2. Implement the Safety Technical Supervision Regulations for Pressure Vessels
3. Adopting the GB150-1998 standard for steel pressure vessels.
4. After the equipment is manufactured, the shell is subjected to a 1.25 times water pressure test.
7、 Benefit analysis
Taking the evaporation capacity of an 80t/h boiler in a thermal power plant as an example, calculate its comprehensive efficiency of pollutant utilization.
The discharge rate is calculated at 2%, and the discharge volume is 1.6t/h
After continuous expansion and evaporation separation of the discharge expansion container (with 50% separation and evaporation of the working fluid), the remaining discharged sewage is 0.8t/h at a temperature of 170 ℃. Then, after regular expansion and evaporation separation of the discharge expansion container (with 50% separation and evaporation of the working fluid), the steam and water enter the low-pressure expansion of the discharge cooler, and the amount of steam separated by evaporation (with 80% separation and evaporation of the working fluid) is 0.64t/h at a temperature of 127 ℃, with an enthalpy value of 2715KJ/kg; The remaining sewage discharge is 0.16t/h, with a temperature of 127 ℃ and an enthalpy value of 529KJ/kg. After cooling, the discharge temperature is 50 ℃ and the enthalpy value is 220KJ/kg. The heat absorbed by the sewage cooler is:
0.64*1000*2715=1737600KJ/h
0.16*1000*（529-220）=49440 KJ/h
If the annual operating time is calculated as 7200 hours, the annual heat absorption of the sewage cooler is:
1737600*7200=12510720000KJ
49440*7200=355968000 KJ
If the calorific value of standard coal is calculated at 29271 KJ/kg, the annual coal savings will be:
（12510720000+355968000）÷29271=439571 kg
≈440T
Standard coal is calculated at a market price of 600 yuan/ton, equivalent to 264000 yuan (264000 yuan) for the people
Based on the above single case analysis, investing in sewage coolers has played a significant role in energy conservation, reducing consumption, improving economic benefits (saving RMB 264000 annually), optimizing the environment, and other aspects. It is a product with dual characteristics of energy conservation and environmental protection.
