Ammonia Process Technology Exchange Area [Daily Question 2009-03-10]

Strengthen the recycling and utilization of waste heat. For example, the CO2 stripping process uses high-temperature temperature-controlled water from a high-pressure scrubber to heat the urine from the distillation section of the low-pressure decomposed distillation tower to save steam consumption. ； For example, some factories use lithium bromide refrigeration technology to recover the heat of hot desalted water from a suction cooler, etc. ； For example, if a 0.6MPa steam expansion tank is added to the aqueous solution process, the high-temperature saturated steam condensate from the shell side of the one-part heater will be used to produce low-pressure steam in the expansion tank for desorption, two-part heater or steam ejector, which can save steam consumption.

We used to use one ammonia cooler for decarbonization, and the outlet of the ammonia cooler fed the ice machine. Later, we transformed it into two ammonia coolers, one to deliver compound fertilizer and the other to deliver ice machine. In this way, the heat energy can be fully utilized, and the load of the ice machine can be reduced a lot. Before the transformation, two ice machines had to be operated. After the transformation, even one ice machine could not reach the full load.

Waste heat boiler can be used for heating, bathing, etc.

I feel that most of them are waste heat boilers, which can be used for heating and bathing. All the ones I have seen are like this.

One section of the furnace in our factory is equipped with six heat exchangers and air steam preheaters.: Increase the temperature entering the second-stage furnace so that it can spontaneously ignite with the hydrogen in the reformed gas ； Raw material steam preheater—increases the temperature of the raw material to meet the reaction temperature ； steam superheater ； Flue waste heat boiler - increase the temperature of the feed water entering the steam drum to produce qualified steam ； Boiler feed water preheater—increases the temperature of the feed water entering the steam drum ； Gas preheater - increasing the temperature of the gas is beneficial to combustion.

There are many ways to utilize waste heat in factories, and the following three are commonly used. 1． Direct Utilization of Waste Heat If there are suitable heat users to directly utilize the waste heat, it is the most economical and convenient. Commonly used hot users include: (1) Preheat air or gas. The waste heat of the flue gas is used to preheat the combustion air or low calorific value gas of the industrial furnace through a heat exchanger (air preheater, etc.). Return heat to the furnace, while improving combustion temperature and combustion efficiency, saving fuel consumption. (2) Preheat or dry materials. Using the waste heat of flue gas to preheat and dry raw materials or workpieces, and bringing the heat back into the device, can also directly save energy. (3) Produce steam or hot water. The waste heat of the flue gas is recovered through the waste heat boiler to generate steam or hot water for production process or daily needs. Cooling water with a temperature above 40°C can also be used directly for heating. (4) Waste heat cooling. Use low-temperature waste heat or steam as the heat source of the absorption refrigerator to heat the solution in the generator, evaporate the working fluid, and achieve the purpose of refrigeration through the refrigeration cycle. When heat users decrease in summer and waste heat is abundant, waste heat cooling can be regarded as a way to effectively utilize waste heat. 2. Waste heat power generation is an advanced energy that is easy to use and flexible. For high-temperature waste heat, the use of waste heat power generation system is more in line with the principle of energy level matching. For lower-temperature waste heat, converting the waste heat into electrical energy for reuse is also an optional recovery solution when there is no appropriate heat user. There are several ways to generate electricity from waste heat:: (1) The waste heat boiler is used to first generate steam, and then it is passed through the steam turbine generator unit to generate electricity according to the cycle of the condensing unit or the back-pressure heating unit. (2) Use high-temperature waste heat as the heat source of the gas turbine working fluid. The pressurized and heated working fluid drives the steam turbine to do work, driving the compressor to work and at the same time driving the generator to generate electricity. (3) Use low-boiling point working fluid to recover medium and low-temperature waste heat. The generated low-boiling point working fluid vapor expands in the turbine according to the Rankine cycle to drive the generator to generate electricity. 3． The heat pump system can use the low-temperature waste heat that cannot be directly utilized as the low-temperature heat source of the heat pump system, raise its temperature level through the heat pump, and then utilize it. In addition to the above three methods, according to the specific conditions of waste heat resources, a comprehensive utilization system can also be considered to make the best use of heat. For example, the multi-stage utilization of high-temperature flue gas waste heat not only preheats air, but also supplies waste heat boilers to generate steam. ； When recovering steam power, the steam parameters should be increased as much as possible, and a combined heat and power cycle unit should be used to generate heat while generating electricity. ； For high-temperature exhaust gas with a certain pressure, it can first be expanded by the gas turbine to do work, and then the exhaust gas can be used to supply the waste heat boiler. The steam generated in the waste heat boiler can also be used by the steam turbine to expand and do work, forming a gas-steam combined cycle to improve the utilization rate of waste heat. When comparing different waste heat recovery options, the basic principle is: Recycling efficiency is as high as possible ； The recovery cost is as low as possible, or the investment payback period is as short as possible ； Strong ability to adapt to load changes.

For synthesis reaction heat recovery, the 10.5MPA high saturated steam by-product of the waste heat boiler is first removed. After being overheated in the superheated furnace, it is sent to the high-pressure superheated steam pipe network for use by the steam turbine. Then, gas-to-gas heat exchange is performed to increase the temperature of the gas entering the tower. In other positions, there are by-products of low-pressure steam, boiler water preheating, and HVAC water supply.