Indirect Cooling Method:
The refrigerant used is a mixture of ethanol or glycol and water. It is cooled in the evaporator box of the ammonia refrigerator and the temperature is typically controlled at around -5°C. The refrigerant enters from below and exits from above.
Direct Cooling Method:
In this method, the refrigerant in the cooling jacket is liquid ammonia, which flows in either a vertical or horizontal flow type in a semi-circular tube. The liquid ammonia enters from above through the distribution tube and flows downwards.
Comparison of the Two Cooling Methods
Compared to indirect cooling, direct evaporative cooling using liquid ammonia has the following advantages:
1. Energy savings of approximately 20%. The compressor operating temperature for direct evaporation is only about -5°C. In contrast, indirect cooling requires the compressor to operate at a much lower temperature, resulting in a lower refrigeration capacity of the chiller. Additionally, the use of liquid ammonia as the refrigerant allows for smaller quantities to be delivered.
2. Less equipment is required. Direct cooling eliminates the need for alcohol or glycol water required in indirect cooling, as well as the need for an evaporator.
3. Fewer insulation materials are needed, leading to lower installation costs. The reduced flow of liquid ammonia allows for smaller pipe diameters and containers, reducing the consumption of insulation materials and saving on installation costs.
The Safety of Using Liquid Ammonia
Due to these significant advantages, an increasing number of breweries are adopting liquid ammonia direct evaporative cooling. However, several aspects need attention when using direct cooling:
1. Firstly, liquid ammonia has an irritating odor and can be flammable and explosive under certain conditions. Its toxicity and safety must be considered during the design process.
2. Secondly, liquid ammonia operates at high working pressures and has strong permeability. Therefore, the welding quality of the fermenter’s jacket is crucial.
3. The structure type of the jacket and the welding quality are key factors in achieving successful direct cooling of the fermenter.