Simdean were asked to explore ways of overcoming a temperature issue at the client’s fish-processing plant in Aberdeen. The plant takes fish trimmings from all over Scotland and converts them into high-grade fish meal and fish oil. The trimmings come mainly from herring, mackerel, cod, haddock and salmon.
Part of the plant’s processing system involves the use of evaporators from which exhaust gases are led to on-site steam boilers via a seawater scrubber. The scrubber is used to remove ammonia and other contaminants from the gases on a once-through basis. It is then returned to the sea via a pumped pipework system. The problem was that at times of high throughput the seawater temperature was coming very close to the allowed return temperature set by SEPA (Scottish Environmental Protection Agency).
Simdean were briefed to look at ways of reducing the return temperature of the seawater during these periods of high throughput.
The exhaust gases exiting the evaporators have a high moisture content and are almost saturated at approximately 85°C – 95°C. This gives them a high degree of latent heat. Our proposal for removing the heat, which was accepted by the client, was a ‘run-around’ system made up of an air to water heat exchanger linked via circulating pumps to a dry air cooler. The system was designed to remove 800kW from the gas stream during maximum output from the evaporators. Because of contaminants within the stream, the heat exchanger and all ductwork/pipework were constructed from stainless steel.
The system was commissioned in August 2015. Although it was designed to provide a minimum heat recovery rate of 800kW, its actual recovery rate was equivalent to approximately 2 MW, which reduced the temperature of the seawater return to well below that required by SEPA.