Under environmental protection pressures, how can we solve the challenge of heat sources for grain dryers?

In recent years, China has stepped up its efforts to strengthen environmental protection across the country, particularly in addressing and preventing industrial pollution emissions, achieving initial successes. However, this shift has also inevitably brought challenges for certain industrial sectors. Take the grain dryer industry as an example: the heating system is a critical component of grain dryers, and traditionally, coal has been the primary source of heat for these machines. With the implementation of “coal bans” in various regions, grain dryers have been forced to seek new heating sources to replace coal—a fuel that is relatively highly polluting. This development has presented a new challenge for grain dryer manufacturers nationwide. For a long time, the grain industry has been characterized by low value-added products, with industry growth consistently driven by “high volume, low margin” strategies. As a traditional energy source, coal has long been favored for grain dryers due to its low cost and easy availability. Yet, under mounting pressure from national environmental policies, manufacturers have been compelled to develop alternative energy solutions—ensuring that grain dryers can continue to operate normally while meeting stringent emission standards. Currently, the main alternative energy options available in China include natural gas, air-source heat pumps, biomass pellets, and steam. Below, we’ll introduce these different energy sources, drawing on the 20-plus years of successful experience of Zhengzhou Wanggu Machinery Co., Ltd., a company specializing in grain dryers.

Natural gas is a clean energy source. When burned completely, it primarily produces non-toxic carbon dioxide and water, along with trace amounts of sulfur dioxide and nitrogen oxides. Due to their extremely low concentrations, these emissions have negligible environmental impacts and can be safely ignored. Therefore, the flue gases from natural gas combustion can be released directly into the atmosphere without prior treatment. As a result, gas-fired hot-air furnaces are increasingly being adopted in the grain-drying industry. Users typically obtain their natural gas supply through either fixed pipeline systems or mobile natural gas tankers—non-fixed supply methods.

A steam heat exchanger is a type of heat exchange equipment that uses the heat released during steam condensation to warm ambient air. It boasts advantages such as cleanliness, simplicity, easy temperature control, and straightforward operation. After being heated, the ambient air can be directly used as the drying medium in grain dryers. This method is typically suitable only for scenarios where large-scale industrial steam resources are readily available near grain-drying plant sites—particularly in large-scale grain-processing enterprises that have built their own grain dryers. Such enterprises usually have large steam boilers on-site, with surplus industrial steam available for use. Currently, Zhengzhou Wanggu has successfully installed dozens of steam-powered grain dryers, each with a daily capacity of 1,000 tons, in multiple provinces including Northeast China, Northwest China, and Henan Province.

Biomass pellet fuel is a new type of energy fuel produced by processing agricultural residues such as straw, rice husks, firewood, peanut shells, corn cobs, camellia seed shells, and cottonseed hulls into pellet form. Since biomass pellet fuel contains neither sulfur nor phosphorus, its combustion does not produce sulfur or phosphorus oxides, thus avoiding the formation of acid rain and causing minimal environmental pollution. After combustion, biomass pellets leave very little ash residue, reducing the need for large storage areas for furnace slag. Moreover, the ash left after burning biomass pellets serves as an organic potassium fertilizer that can be recycled to generate additional revenue. Typically, biomass pellets have characteristics such as low bulk density, relatively low calorific value, and a higher concentration of fine particulate dust after combustion. Therefore, the furnace structure of hot-air stoves and the flue gas dust removal systems must be optimally designed to meet both the heating requirements of grain dryers and the stringent environmental standards for dust emissions.

An air-source heat pump is a drying method that uses electricity as its energy source to absorb and convert energy from the air into thermal energy. Thanks to its clean, pollution-free advantages, air-source heat pump technology has gradually been adopted and promoted in the grain-drying industry in recent years. However, due to the inherent limitations of the heat pump’s operating principle, this technology is currently mostly applied to small-scale grain-drying equipment. Moreover, its use is geographically restricted, typically being employed in warmer southern regions—often serving as the primary heat source for low-temperature rice drying.