Double grate combustion, also known as water-cooled grate combustion, is a good combustion for small boilers. Because it has a better effect on smoke prevention and dust control.

Air supplying to the burning layer on water-cooled grate is from the top to the bottom (reverse combustion), and the conventional auxiliary grate is always installed on the lower part of the water-cooled grate. Semi coal gas is the main combustion between two grates. The fine particles on the combustion, when the boiler is in operation. In this way, we may achieve the purpose of eliminating smoke and dust. When combustion layer in water-cooled grate is cleaned, some dust may fly out with smoke and vapor, but this phenomena last only a short time. China owns vast territory, and its economic development is not balanced, advanced dust removal equipment is used when coal-fired boilers in some unimportant areas (suburbs, towns) are adopted, it is not likely to use a large number of fuel gas boilers, therefore, water-cooled grate coal-fired boilers of small capacity have been first developed and used since 40 years ago in Harbin ,China. And this kind of boilers is still being used now.

Furthermore, the heating surface of water-cooled grate has high heat intensity, working together with high heat transfer and the thread smoke tube, can decrease the boiler steel consumption obviously.

In the course of the development of industrial boilers in various countries, the boiler, whose capacity is greater than 1 steam ton (0.7MW), generally does not adopt vertical structure, because although the area is small, but the diameter and height of the shell is too large, which leads to significant waste of steel. In particular, the water-cooling grate, if the furnace is arranged in the internal furnace, the pot shell has a larger diameter; if the grate is external, the advantages of smaller area no longer exists. In addition, there is a problem on the convection heating surface: safety and reliability of vertical smoke pipe’s tube plate is hard to guarantee (water side fouling is difficult to remove) ; horizontal water pipe’s smoke discharging is too slow, so it is difficult to prevent fouling, and heat transfer’s effect is bad.

Based on the above reasons, the 0.35 MW to 0.21 MW water-cooled grate atmospheric pressure hot water boiler adopts the new water pipe horizontal boiler’s structure, whose combustion equipment is water-cooled grate which has 28-year working experience. In order to prevent the smoke pipe inlet temperature is too high, a small amount of water pipe is equipped. The boiler structure is compact, so the whole boiler may leave the factory integrallty. (base is set on the lower part.).

This kind of boiler can develop to the one with larger capacity, but at present, water-cooled grate adopts hand burn method, if the capacity is larger, the stoker must work harder, which limits the further increase of the capacity.

Recycle water of the system enters the water-cooled grate boiler header end from one side of the boiler, flowing through the three return fire grate tube to the back water discharging tubes of the underneath collecting tank from the water-cooled grate boiler header end. Recycle water of the system then flows into both sides of the from the upside collecting tank. Then through aqueduct recycle water of the system sprays to the bottom of the heat pipe cavendish, finally the water enters the discharging tube from the top of the pot shell.