Ohrid conference highlights: ammonia refrigeration in China
Over 92% of Chinese cold stores have adopted ammonia as a refrigerant.
According to Jianji Zhang*, from the College of Mechanical Engineering, Jimei University in Xianmen, series reciprocating compressors are currently the most widely used due to low cost and availability of spares, but screw compressors which have higher output tend to replace them.
Evaporative condensers are now the first choice and widely used in ammonia refrigeration plants. Traditionally shell-and-tube condensers were employed, but the 90’s water shortages led to increasing awareness of the advantages of evaporative condensers in saving water and energy. Evaporators in most freezer spaces adopt cooling coils, which is one of the main differences between Chinese and more developed countries’ ammonia refrigeration systems. Traditionally, wall and overhead cooling coils tended to be used even though wall coils are currently being abandoned in order to save space.
Operational energy efficiency varies greatly: the ratio of the highest to lowest power consumption per unit in different refrigeration plants is between 2.9 and 5.4.
Most ammonia refrigeration plants are not equipped to measure power consumption in important gauging points, indicating a low level of energy management. Most plants also tend to have a huge charge, due to cooling coils which typically have a large internal volumes and low heat-transfer coefficients that represent a safety hazard. Furthermore, many ammonia refrigeration systems are in dilapidated condition sometimes with insufficient funding and poor attention paid to repairs and maintenance. There is also a shortage of protective equipment for working with ammonia. As a result, many accidents in ammonia refrigeration plants have been reported in recent years in China.
A national standard “GB28009-2011 Safety Code for Cold Stores” was issued in December 2011 and came into force in December 2012. According to this document, design, construction and management of cold stores become mandatory topics, which will undoubtedly lead to a reduction in accidents. In addition, other national standards are currently being developed.
Over the past five years, screw compressors were adopted in 60% of new installations, air coolers in 30% and automatic control systems were increasingly used. In 2011, cascade refrigeration plants with ammonia and CO2 were also brought into use, further narrowing the gap between ammonia refrigeration in China and more developed countries.
*Status and Analysis of Ammonia Refrigeration Technology for Cold Stores in China, Jianji Zhang
This paper from IIR Ammonia Refrigeration Technology conference can be downloaded via the IIR’s Fridoc database (free for IIR members within the framework of their quota of free downloads).