)) Achievements and Experiences Improvement of Vacuum Oxygenation and Condensation System Wei Shouwu (Shanxi Coking Co., Ltd., Shanxi Hongdong System's use of surface heat exchangers not only fully meets the previously required process specifications, but also disables fresh water. Recovered the residual heat of steam, improved the working conditions of workers, and achieved better economic and social benefits.
Shanxi Coking Co., Ltd. Power Plant has three 35t/h pulverized coal boilers. The original design used 75t/h atmospheric deaerator. After the company's chemical fertilizer plant is put into production, in order to recover high-temperature waste heat from the fertilizer production process, the soft water sent from the water treatment station is sent to the chemical fertilizer synthesis and purification plant through the preheating line where it absorbs heat from the waste heat exchanger. About l * C, and then sent to the atmospheric deaerator through the return line.
During the operation of the preheating line, we found that the corrosion of the preheating line was very serious. Especially in the return line, the iron ion content in the boiler feed water remained high, and the preheating line leak occurred. The analysis shows that the oxygen content of soft water is too high, especially after the temperature rise, some of the free oxygen is precipitated and the oxygen corrosion is intensified. In order to solve the oxygen corrosion problem of the preheating line, a 100t/h vacuum deaeration device was newly installed in the power plant in 1990 to allow soft water to be deaerated before entering the preheating line.
1 Problems in the original vacuum deoxygenation operation The original vacuum deaeration device Under the action of a three-stage steam ejector, a vacuum can be generated in the vacuum deaerator to allow normal-temperature water to boil. In this way, the soft water from the soft water station is boiling, the partial pressure of water vapor increases, the partial pressure of oxygen decreases, the dissolved oxygen continuously overflows and is extracted, so as to achieve the effect of removing oxygen. After the steam has passed the ejector work, it is mixed with fresh water at a temperature of 14"C in the first, second and third condensers. The condensate of the condenser is mixed with the cooling water and discharged into the trench. However, in the actual operation, the following Problem: Condenser drain plugs are severe due to mixed heat transfer between the waste steam and cooling water in the condenser. During the heat exchange process, the temperature of the cooling water rises, temporarily reducing the hardness of the fresh water used for the cooling, and the calcium and magnesium ions are Precipitation precipitates and gradually deposits on the water distribution plate and the outlet pipe wall of the condenser, so that the outlet flow area is reduced or even blocked, the condenser does not work properly, resulting in a decrease in the degree of vacuum in the deaerator, and the oxygen content of the effluent exceeds the standard. In actual production, it is necessary to perform a parking treatment once every 23 months to clean up the scale.
Fresh water consumption is large. The condenser is cooled with fresh water. The original designed cooling water volume is 50 t/h for the primary condenser, 30 t/h for the secondary, and 16 t/h for the tertiary. In this way, although the third condenser is not required to be used in actual operation, Cooling water, but the primary and secondary condensers still consume 25.3 million tons of fresh water each year. The cooling water discharged is of good quality, and the temperature is about 2CTC, which causes huge waste. It is a pity.
The waste heat of steam is not utilized. The vacuum deaeration consumes 500,700kg/h of medium pressure steam. After the steam generated by the ejector, the steam condenses and is drained with the cooling water. The steam loss is more than 5 000 tons per year. The loss of heating value 2 reconstruction program must first completely solve the vacuum deaeration condensation system. Scaling problem, prevent the plugging of the sewage system, secondly, it is better to disable fresh water, and to recover the waste heat as much as possible, strive to reduce the remodeling of the fresh water and steam, reconstruct the pipeline and equipment, the original pipeline and equipment consumption. . The transformation diagram is as follows: The first and second condensers are replaced with surface heat exchangers, and the series operation mode is adopted; the soft water from the water treatment station is used as the cooling medium, and the soft water is sent to the vacuum deaerator after being heat-exchanged by the condenser.
The reformed steam condensate will not be recycled, and the third-stage condenser will not cast cooling water, which is the same as the current operating mode.
Design, make a new condenser, remove the original hybrid condenser and all fresh water lines.
After the condenser is replaced with surface cooling, the heat exchange efficiency will be reduced and the condensation effect will be affected. Therefore, the key to the transformation is to condense the waste steam discharged from the ejector and the steam extracted from the deaerator. A sufficient degree of vacuum must be created, that is, the temperature in the condenser is ensured to fall below the saturation temperature required for absolute pressure. For this purpose, make the following calculations to determine the operating parameters.
After checking the original vacuum deaeration thermal calculation book, the first condenser condenser condensing vapor volume is 349.4kg/h, condenser absolute pressure = 8.55kPa, the corresponding saturation temperature such as = 42. 51:, total gas volume = Air extraction volume + working steam volume = 141 + 250 = 391 kg/h. The amount of steam that the secondary condenser needs to condense is 184. The absolute pressure in the condenser is 2 = 28.9 kPa, corresponding to the saturation temperature. 2 = 68 = C, total gas volume = pumping volume + working steam volume = 61. The parameters for vacuum deaeration operation are as follows: The total working steam volume is 500600 kg/h, and the intake air temperature of the "class condenser" is 7 ( TC, the inlet temperature of the secondary condenser is 160X:.
According to the actual situation of the workshop, the soft water flow in winter is generally 130t/h, the summer flow is about TOt/h or more, the calculated amount of cooling water is 7t/h, and the soft water outlet temperature of the water treatment station is about 2CTC. The quantity is larger than the secondary condenser, taking into account the convenience of the production of spare parts during operation, so the design of the condenser uses a secondary condenser as the design object, and the same heat exchanger is used for the primary and secondary condensers.
According to the conditions, after design calculations and calibration calculations, the condensers were designed as follows: heat transfer area 39m2, heat exchange tube size 25X2.5X2000mm3, heat exchange tube 261, heat exchanger inner diameter 600mm. 3 transformation effect transformation work in 2003, year Completed in July, the vacuum deaeration was successful. The deaerator head pressure reached 5.OkPa within a few minutes after driving, and the dissolved oxygen content quickly dropped to 50fxg/L. After several hours of operation, the dissolved oxygen content dropped to 30;xg/L, deoxygenation pressure is 4.OkPa. After several months of trial operation, the current oxygen content of the water is stable at 15g/L, all the technical indicators have reached the design requirements, and the transformation has made great success.
After the transformation, the vacuum deaeration system completely stopped the use of fresh water, saving about 35 tons of water per hour, and saving more than 250,000 tons of water every year. According to the company's price of 0.73 yuan/t, it saved 228,800 yuan of water annually. According to the soft water flow rate of 70t/h, after passing through the two-stage condenser, the water temperature rises by 51: and the heat recovery is 3.05X109kcal, which is equivalent to 600t thermal coal. The fuel cost is RMB 90,000 per year if it is calculated as 150 yuan per ton. . The total annual economic benefit can reach more than 310,000 yuan.
After the vacuum deoxidation and condensing system was changed to soft water, the scaling problems of the condenser, the water pipeline, and the diffusion tube of the steam ejector were completely solved, the operation was stabilized, and the labor intensity of the inspection workers was reduced; at the same time, the vacuum deoxidation process operation was also improved. Simplification, no need to adjust the amount of fresh water, greatly reducing the labor intensity of the operator. In addition, the waste heat from the steam was recovered and the fresh water was stopped, reducing a lot of sewage and waste heat pollution.
Samples from Sleevewood* "Shencheng People's Green Power Available During the Year Shanghai Green Power will achieve a breakthrough of zero. Four wind power generating units totaling 3,400 kilowatts and a 10-kilowatt solar photovoltaic power generation system have been invested in the coastal area of ​​Fengxian. The trial operation will formally be connected to the grid for power generation this year, when Shanghai citizens will use “green power†for the first time, and Fengxian’s “power reserve†in the coastal area will generate about 7.6 million kWh of power. By the end of 2004, the total installed capacity reached 20,000 kW. The Chongming and Nanhui wind farms will also be put into operation. The annual power generation is about 50,000 due to the high cost of green electricity. Currently, the on-grid tariffs for the Chongming and Nanhui wind farms approved by the state are at 675 yuan/kWh, much higher than the city's. The average on-grid tariff is 0.31 yuan/degree, and the government is trying to reach out to domestic and foreign companies that are interested in this business.The companies that are willing to buy green power will issue relevant honor logos.
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