(1) Technical scope of application

(1) Technical scope of application

It can be applied to the heat of high-temperature or medium-temperature flue gas generated in industrial kilns, boilers, coking furnaces, blast furnaces, and metallurgical furnaces. It is exchanged through heat exchangers to recover its heat, heated water or air, and the generated hot water, steam or high-temperature air can meet the needs of domestic hot water, heating, power generation steam, or food and material drying.

(2) Technical principles (transformation content)

① Introduction to boiler steam recovery technology

When the system is running, condensed water is discharged from the heat-using equipment and enters the steam recovery machine through the steam trap. The steam recovery machine consists of a flash tank, a dirt remover, a condensate quick drainage device, a pressure balance device, a cavitation eliminator, a water storage tank, a liquid level transmitter sensor, etc. When the high-temperature condensed water enters the flash tank, steam and water separation is carried out in the tank. The condensed water flows into the water storage tank through the quick discharge device, and the produced secondary gas is sent to the condensate water pump outlet pipe through the ejector device, so that the flash steam can be hermetically recovered. Due to the continuous removal of gases and liquids in the flash tank, the pressure in the flash tank is always kept lower than the pressure at the condensate outlet of the heat-using equipment, thus ensuring that the backwater back pressure can be smooth even under low conditions.

The flash tank and the water storage tank are connected through a quick drain device. In order to allow condensed water to flow into the water storage tank quickly, a pressure balancing device is operated in the tank. Under normal circumstances, the working pressure of the steam recovery machine is set below 0.1MPa. In actual selection, the working pressure in the box will be selected according to the level of the return water back pressure, so that the box will always remain sealed and blocked from the atmosphere. The two-phase fluid of steam and liquid in the water storage tank is regulated by the pressure balance device to form a certain pressure on the liquid surface. Through the cavitation eliminator, the condensate pump changes the water pump during the process of sucking in high-temperature condensate water. The conditions for occurrence of cavitation ensure that the entire backwater is in closed operation and the condensate pump of the steam recovery machine does not occur. According to the actual needs of each system's working conditions, we can divide the pump operation mode of this equipment into two types: one is continuous movement, which is mainly used when the requirements for continuity of water supply are quite strict; the other is intermittent operation, and the pump is set according to the fullness of condensed water in the water tank. The steam recovery machine has manual and automatic dual control methods in the same electrical control cabinet. When automatic is set, the water pump starts when the liquid level is high and stops when the liquid level is low. When the water level in the water storage tank exceeds the high water level line, the water pump starts, and stops when the water level reaches the lower limit. If a system fails, a sound and light alarm will be automatically issued. During normal operation, the two pumps will switch regularly.

② Principle of power saving

The new equipment increases the heat exchange area of the device, which is 24.3% higher than the original equipment, making the outlet temperature of AB23WA103 heat exchange equipment increase by about 15 ° C. The device can make full use of 1.5barG waste heat steam, thereby saving the use of 5bar steam in the secondary solution evaporator and achieving the purpose of energy conservation.

By changing the technical transformation of the melt melting section of the BPA plant, the originally used medium pressure steam was replaced with 1.5 barG steam that was a by-product of the reaction heat of the adjacent plant to meet the melting requirements of the production process. In addition, by using 1.5 barG steam to preheat the feed of the tower, from the perspective of energy balance, the consumption of 5barG steam in the reboiler is reduced by increasing the enthalpy of the feed. Both aspects are conducive to reducing the amount of purchased steam.

(3) Application cases

A: Covestro Polymers (China) Co., Ltd. solution evaporator to increase heat exchange area to save steam

Implementation content and cycle: This renovation replaces AB23WA103 equipment, increasing the heat exchange area of the equipment. In this way, 1.5 barG of waste heat steam can be fully utilized in the primary solution evaporator, thereby reducing the use of 5barG steam in the secondary solution evaporator. The working principles of the old and new equipment AB23WA103 are completely the same. The difference is that the new equipment increases the heat exchange area, which is 24.3% higher than the heat exchange area of the original equipment, which increases the outlet temperature of the AB23WA103 heat exchange equipment by about 15 ° C. The project starts in September 2020 and will be completed in December 2020.

Energy conservation and emission reduction effect and investment payback period: The energy conservation amount of this project is 258tce. Based on the calculation of 250 yuan per ton of steam, the project saves 2737 tons of steam, which saves 684,000 yuan per year. Therefore, the investment payback period of this project is 700.22/68.4=10 years.

B: Line 6/7 of the BPA plant of Covestro Polymers (China) Co., Ltd. uses waste heat of 1.5barg steam to melt the melt and preheat the tower feed project.

(1) Implementation content and cycle: A new 1.5barG steam transmission pipeline will be built to send the 1.5barG steam generated by the exothermic reaction of adjacent units to Line 6/7 of the BPA unit, and the melt melting section in the unit will be transformed. A new circulation loop for molten products will be built, which will directly contact the melt to melt them. The required heat is supplied from 1.5barG steam through the heat exchanger, reducing the original use of 20barG steam.

On the feed side of the mother liquor dehydration tower, in addition to retaining the original heat recovery heat exchanger for the bottom product of the tower, a new heat exchanger is added, and 1.5 barG steam is used to provide heat to increase the temperature of the material entering the tower, thereby reducing the consumption of 5barg steam in the tower. The start date of the project is August 17, 2019, and on-site construction will be completed and put into use on June 23, 2020.

(2) Energy conservation and emission reduction effect and investment payback period: Based on 250 yuan per ton of steam, the project saves 31337 tons of steam, which saves 7.834 million yuan per year. Therefore, the investment payback period of this project =388.45/783.4=6 months.

(4) Potential for replication and promotion, energy-saving potential (payback period)

Energy-saving transformation of some waste-heat generation systems can bring huge economic benefits. Steam recoverers and other equipment can be safely and reliably applied to waste-heat recovery technology. The technological transformation method is safe and reliable, and can effectively utilize the waste-heat steam of the heating furnace., etc., has huge energy-saving potential, obvious energy-saving and emission reduction effects, broad promotion and application prospects, and huge replication potential.