What is 3 Pass Water Tube Boiler?

The single-pass, double-pass and three-pass in a steam boiler are actually similar to the return in a heat exchanger. They mainly refer to the number of cycles of water pipes in the boiler furnace. For single-pass, it means one in and one out. The return journey is two in and two out, and the three return journey is one more cycle.

Gas boilers are also divided into many types. Among them, according to the flue gas process, they are divided into two-pass gas boilers and three-pass gas boilers, mainly WNS series shell type wet back furnaces.

First return: The corrugated furnace combustion chamber transfers radiant heat through the furnace wall
Second return: the threaded smoke tube bundle area located on both sides of the furnace
Third return trip: the light tube bundle area located above the furnace

The difference between two pass boiler and three pass boiler
1. In terms of structure, there is one more heat exchange area for the three-pass than the two-pass. The most direct way to judge the shape is to look at the position of the boiler’s smoke outlet. The smoke outlet at the opposite end of the burner is a three-pass boiler, and at the same end of the boiler burner is a two-pass boiler!2. In the system, an economizer is added at the end of the three-pass to further absorb the flue gas temperature and reduce the exhaust gas temperature. The second-pass condensing boiler adds an economizer and condenser, which has a larger heat absorption surface and a lower exhaust gas temperature.
2. There is little difference in cost. The three-pass boiler body adds a threaded smoke tube area, which uses more materials than the two-pass boiler, but the second-pass boiler stretch rod (fixing effect) is more than that of the three-pass, and the second-pass is more expensive than the three-pass, which leads to the overall system cost. no big difference.
3. In terms of performance, both thermal efficiency is relatively high, as high as 98%.

Therefore, the first consideration for users to choose a boiler is whether the main parameters such as the boiler’s thermal efficiency, exhaust gas temperature, and flue gas emission indicators can meet the actual needs of the enterprise, combined with the comprehensive judgment of the manufacturer’s strength!