(1) Technical scope of application

(1) Technical scope of application

This technology is mainly used in the chemical industry.

(2) Technical principles (transformation content)

① Technical introduction

A newly installed lithium bromide refrigerator and a supporting 0.5barg steam and condensed water pipeline system will be connected to the lithium bromide refrigerator to make better use of the excess 0.5barg steam. Use excess 0.5barg steam from MDI and MMDI units to connect to the lithium bromide refrigerator generator to evaporate the lithium bromide solution water. Under normal operation of MDI and MMDI units, the lithium bromide refrigerator was directly operated and an electric refrigerator was stopped.

② Energy saving principles

In lithium bromide absorption refrigeration, water serves as the refrigerant and lithium bromide serves as the absorbent. Since the boiling point of the lithium bromide aqueous solution itself is very high and is extremely difficult to volatilize, the vapor on the liquid surface of the lithium bromide saturated solution can be considered to be pure water vapor.

The MDI device and MMDI device operate very stably, allowing the excess 0.5 barg of steam generated to be stably supplied to the lithium bromide refrigerator, thereby reducing the operation of an electric refrigerator. The lithium bromide refrigerator system itself has excellent operating reliability. Even if the MDI device and the MMDI device are unable to supply 0.5 barg steam due to the skipping of the MDI device and the MMDI device, the lithium bromide refrigerator can automatically be in standby mode. The operation in the central control room only needs to be carried out from the lithium bromide refrigerator. The chilled water regulating valve coming out of the refrigerator can be controlled to an appropriate opening to ensure the supply temperature of other chilled water users. The freezer automatic control system will automatically sense the recovery of 0.5barg steam. Once the steam recovers, the freezer will resume work without disturbance. Therefore, this project saves electricity consumption by utilizing waste steam.

(3) Application cases

Covestro Polymers (China) Co., Ltd. MDI lithium bromide refrigerator renovation project.

1) Implementation content and cycle: 0.5barg of excess steam generated during the production process of MDI and MMDI units is cooled by air coolers and water coolers and then recycled condensed water. The freezer of the original MDI device was electrically driven. A newly installed lithium bromide refrigerator is used for this project. Excess 0.5barg steam from MDI and MMDI units is connected to the lithium bromide refrigerator generator to evaporate lithium bromide solution water. Under normal operation of MDI and MMDI devices, an electric refrigerator can be shut down to achieve energy conservation. The cycle is 8 months.

2) Energy conservation and emission reduction effect and investment payback period:

Electricity consumption per unit of cooling capacity before renovation =1482.73÷7485.01=0.198 million kWh/(ten thousand kWh of cooling capacity)

Electricity consumption per unit of cooling capacity after transformation =339.35÷3381.94=0.1 million kWh/(ten thousand kWh cooling capacity).

Therefore, annual electricity saving of the project =(unit consumption before transformation-unit consumption after transformation)*Refrigeration capacity before transformation =(0.198-0.1)*7485.01= 7.335 million kWh.

The rated power of the condensate pump is increased to 7.5kW for the project. Based on the annual operation of 8000 hours, the power consumption of the pump is 7.5*8000÷10000= 60,000 kWh.

Project energy conservation =(733.5-6) 10,000 kWh *2.88tce/10,000 kW=2095tce (rounded).

The payback period is 4 months.

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

This technology is applied to energy-saving technical transformation of refrigeration units in the chemical industry. Through technical transformation, excess steam and steam energy loss can be fully utilized. The technical transformation method is safe and reliable, the energy-saving and emission reduction effects are relatively obvious, and the potential for promotion, application and replication is relatively large.