Constant pressure method

Scope: The constant pressure method in the biomass boiler heating system in the heating system: In the high-temperature hot water supply system, because the water temperature is higher than the saturation temperature of water under normal pressure, the pressure in the system should be higher than the corresponding water supply temperature Saturation pressure, so as to avoid hot water vaporization and water shock. Water is a non-compressible fluid. Once it leaks, it will drop its pressure. On the contrary, water heating will shrink in volume. If the pressure cannot be stabilized, it will also destroy the equipment in the heating system. Therefore, in order to avoid pressure reduction and vaporization and contraction and pressure increase, the high-temperature hot water system must stabilize the pressure in the system, which is the constant pressure. There are several ways of constant pressure for hot water heating system:

1) Adopt the constant pressure method of elevated water tank

The fixed pressure point of this method is set on the main line of the hot water circulation pump inlet or return water, and the installation is only an elevated water tank. Its structure is simple, the work is stable and reliable, the system pressure can be stabilized, and the system network can meet the overflow and Replenishment request. In this system, the height of the water tank device must meet the requirement of non-vaporization at the highest point in the system. Therefore, the device position is higher. This constant pressure method is suitable for low-temperature water heating systems with a small heating range.

2) Adopt the constant pressure method of make-up water pump

When the pressure of the heating system is high, the use of an elevated water tank cannot guarantee the pressure required by the system. At this time, the constant pressure method of the makeup water pump should be used. This constant pressure method is widely used in Soviet hot water boiler heating systems. The constant pressure of the make-up water pump has two modes: continuous water supply and constant pressure and intermittent water supply and constant pressure. The installation of this biomass boiler in constant pressure mode consists of a make-up water tank, a make-up pump, and a pressure regulator. When the system is operating normally, the pressure regulator adjusts the water supply pump to continuously replenish water and make it compatible with the leakage of the system, thereby maintaining the stability of the system pressure. When the circulating water pump is stopped, the shut-off valve in front of the pressure regulator can be closed. The make-up water pump continues to make up water to maintain the static pressure required by the system. This kind of constant pressure method does not need to shrink the water tank, so the equipment cost is low. In addition, the make-up water pump replenishes water and constant pressure, the power of the water pump is not large, and the operating cost is small. Therefore, this method is quite common in our country’s hot water heating system. The biggest drawback of this constant pressure method is that if the system suddenly loses power, the make-up water pump will lose the constant pressure function. In order to avoid the boiler water shortage and vaporization at this time, the system adopts the pressure water supply auxiliary installation. When the circulating water pump is running, due to the water supply auxiliary installation, the circulating water will not be poured back into the pressure rise system. When the circulating water pump and the make-up water pump are shut down due to a sudden power failure, the pressure water supply system is immediately put into operation, the check valve is automatically opened, and the pressure water will flow through the hot water boiler and be discharged from the gas collecting tank, thereby preventing the furnace chamber The residual heat caused the boiler water to vaporize. At the same time, the main valve of the supply and return hot water pipes should be closed to isolate the heat source from the heating network. The continuous water supply and constant pressure of the biomass boiler feed water pump is controlled by the electric contact pressure gauge. The inlet pressure of the circulating water pump can be maintained within a certain range. When the pressure is lower than this range, the electric contact pressure gauge will act and connect the feed water pump motor circuit. When the make-up water pump is running to make up water, the inlet pressure of the hot water circulation pump rises and exceeds a certain range, the pressure gauge of the hot water boiler cuts off the power supply of the make-up water pump, and the make-up water pump is out of operation. With such reciprocating action, the water supply pump continuously replenishes water and maintains the system pressure to fluctuate within a certain range. In this way, the constant pressure mode of the system, due to continuous water replenishment, saves electricity compared to continuous water replenishment, but its conditioning and constant pressure quality are worse than continuous water replenishment mode. There are also defects such as large pressure fluctuations, frequent contact of the pressure gauge and easy damage.