【HaiChuan Discussion】Which companies use recycled ammonia water waste heat for cooling, and what are the results?

Shaanxi Shanjiao Chemical Co., Ltd. 2019-04-02 Recently, the company’s energy-saving project aimed at utilizing the waste heat from recycled ammonia water was officially launched. This project involves upgrading two sets of refrigeration units that use recycled ammonia water; by removing the existing two 3.5 million Btu steam-based refrigeration units, two new refrigeration units capable of utilizing waste heat from recycled ammonia water with a capacity of 4 million Btu each will be installed, along with a waste heat utilization monitoring system and a remote control system. This project actively responds to the company’s call for improving efficiency and enhancing the comprehensive utilization of energy; by employing technological innovations, it replaces old, energy-intensive equipment, thereby achieving cost reduction and improved efficiency. The project modification involves using recycled ammonia water as a heat source instead of steam for cooling, which solves the problem of corrosion of the piping caused by direct use of recycled ammonia water in the units, as well as the issue of fouling in lithium bromide absorption units and the operational safety concerns associated with the original process system. This approach also helps to reduce operating costs effectively. It is understood that the preliminary construction for this project began in early April, and it is expected to go into operation in May. Once operational, it will enable the savings of 36,720 tons of steam per year, resulting in energy-saving benefits amounting to 3.26808 million yuan per year, **thereby improving the economic efficiency of the enterprise. (Production Operations Department: Wang Sujuan)

What are the technical characteristics of the waste heat recovery refrigeration technology using circulating ammonia water? It is understood that the sensible heat of coking raw gas accounts for about 36% of the heat generated by the coke oven, with most of this heat being absorbed by the sprayed recycled ammonia water. The waste heat recovery refrigeration technology using circulating ammonia water can be used in lithium bromide refrigeration units that utilize circulating ammonia water as the driving heat source to produce low-temperature water. This approach not only enables efficient and safe recovery of the sensible heat contained in waste gas but also helps to improve existing production processes and increase production capacity. This is mainly reflected in the following aspects: First, it reduces the temperature of the circulating ammonia water used for spraying in the coke oven bridge pipes and gas collection pipes, thereby increasing the ability of this circulating ammonia water, as a heat-absorbing medium, to absorb the residual heat from the high-temperature raw gas during atomization ； Secondly, it reduced the temperature of the raw gas before the primary cooler (by 2–4°C), thereby reducing the cooling load on the primary cooler as well as the load on the electrostatic precipitators; it also decreased the amount of water used in the process cycle and the pressure drop across the towers ； Thirdly, the tar content in the gas after electrostatic capture decreases, while the tar yield increases ； Fourth, it improved the operating conditions of the cold blower.

Negative pressure ammonia distillation: This negative pressure distillation process utilizes the principle that different components in a liquid mixture have varying volatilities, and that the boiling point of a liquid decreases as pressure drops. The liquid mixture is preheated to a certain temperature and then fed into a negative pressure distillation tower, where distillation takes place under negative pressure; simultaneous heating at the bottom of the tower helps to separate the various components of the mixture. This technique allows for lower operating temperatures, thereby achieving energy savings and reduced consumption. Process flow for ammonia distillation under negative pressure using coke oven flue gas as a heat source: The remaining ammonia water is heated through a heat exchanger before being sent to the ammonia distillation tower for distillation. The ammonia vapor at the top of the tower is cooled by a decompressor and a cooler; the resulting cooled ammonia water enters the reflux tank. The non-condensable gases at the top of the tank, driven by the vacuum generated by the vacuum device, are cooled by a cooler before entering the coal gas suction pipeline ； The ammonia at the bottom of the tank is pumped out using a reflux pump; part of it is sent back to the top of the ammonia vaporization tower for reflux, while the rest is exported as product ammonia. The ammonia vaporization wastewater from the bottom of the ammonia vaporization tower enters the flue gas heat pipe exchanger, where it is heated cyclically before being returned to the ammonia vaporization tower ； Another portion of the ammonia-vaporized wastewater is cooled by heat exchange with the remaining ammonia solution in the raw material, and then sent to the wastewater treatment facility.