Installation of Make-up Gas Chiller at Suction of Synthesis Gas Compressor at Ammonia Plant

Background

The compressor is the heart of nitrogenous fertiliser plant and is used for various purposes such as compressing the synthesis gas, air, re-cycle gas and ammonia. The compressor capacity is also one of the important parameters controlling the capacity of the plant. Hence, the design of the compressor and its effective utilisation is essential for achieving higher production and lower energy consumption.

The compressor is a constant volume equipment and hence the capacity of the compressor can be increased by increasing the density of the gas at the suction of the compressor. As the gas density is inversely proportional to the temperature, there is a good possibility of increasing the capacity of the compressor by cooling the inlet gas.

This case study describes one such project taken up and implemented successfully in a fertiliser plant.

Previous status

This case study pertains to a ammonia fertiliser complex producing 900 tons per day of Urea. The plant was operating at about 920 TPD of ammonia production. The synthesis gas was entering the compressor at about 39°C.

Energy saving project

The plant installed a vapour absorption refrigeration system with LP steam for cooling the synthesis gas.

Implementation methodology & time frame

The implementation of this project was taken up when the plant was in operation. The hooking up of the new system with the existing was done during the planned shut of the plant. The installation of the new system and successful commissioning took about 18 months. No problem was encountered during the implementation and subsequent operation of the plant.

Benefits of the project

The implementation of this project resulted in the following benefits.

Parameter - Before Implementation - After Implementation

Ammonia Production - 920 TPD - 944 TPD
Syn. gas temperature - 39°C - 13°C
Syn. gas compressor speed - 13,142 RPM - 13,071 RPM

The implementation of this project resulted in a saving of 28,035 GCal per year, which amounted to 0.09 GCal / ton of ammonia.

Financial analysis

The implementatio n of this project resulted in a net annual saving (@ Rs. 350 / GCal) of Rs. 9.8 million. The investment made was about Rs. 22.0 million, which got paid back in 27 months.

Benefits of chiller at suction of synthesis gas compressor

Increase in capacity of compressor
Increased ammonia production
Reduction in specific energy consumption

Cost benefit analysis

Annual Savings - Rs. 9.8 million
Investment - Rs. 22.0 million
Simple payback - 27 months