In the design of atmospheric heating boiler room, the circulation water pump should be selected according to the characteristics of the system and the hydraulic conditions, and the volume and height of the expansion tank should be calculated. The current heating design manual and professional textbooks have not yet been discussed. This paper makes a preliminary discussion on the above problems combined with the practice of engineering design.
1, the atmospheric boiler heating system in accordance with the product samples provided by the boiler manufacturer, there are mainly two forms in the engineering design of the atmospheric boiler heating system.
A) the boiler does not bear the pressure of the system, that is, the backwater first comes to the pressure relief tank and then enters the boiler to heat, as shown. This system fully embodies the characteristics of the normal pressure boiler, and the application is not restricted by the height of the building.
B) boiler in low position, system form and pressure boiler heating system, as shown.
In this system actually becomes a normal pressure boiler pressure boiler, the same system design and general design of heating system, but should pay attention to the selection of 2 atmospheric pressure bearing capacity of the boiler heating boiler room circulating water pump of the heating system in the low atmospheric pressure boiler and pressure boiler heating system, so we only discuss shown not withstanding the system pressure atmospheric pressure boiler heating system.
The system has shown the circulating pump to start from the stable operation process is: the water expansion tank to circulating pump extraction in the boiler, so that the water level in the boiler gradually from H3 to H4, the pressure relief tank float valve gradually opens, the expansion tank water level rises by the circulating water pump before the start of the H2 to the Hi system into the circulation.
1, Gao Dongming, male, born in September 1963, coke Chichiawan University, vice president and 730020 senior engineer Bachelor of engineering of Lanzhou City No. 424 Lanzhou Military Region Air Force reconnaissance and Design Institute (0931) 8950755:2002-01-09 M. Hi head loss, so type (5) can be written as: when the pump stops running, with the expansion tank and the pressure relief tank between the pressure relief tank gradually back to the expansion tank water, expansion of water level in the water tank decreased from Hi to H2 (density changes ignore system water) the water level in the boiler gradually increased from H4 to H3, boiler water float valve shut down. The pressure difference between the expansion water tank and the pressure relief water tank is gradually returned to the pressure relief tank.
In the circulating pump to start the expansion tank water supply, according to the Bernoulli equation, the energy equation can be listed in section A-A and section between: H3 section B-B, A-A from the reference plane (ground) height, m; vavb system startup section A-A, B-B averaged G -- gravity acceleration, m2/s; H cycle the pump head, m; AH1 - A-A water, head loss, pipe and boiler section B-B: m due to the pressure tank and the expansion of the water flow velocity is smaller than the va=0vb= to facilitate the analysis, so the height of M; vavc circulation system, A-A section, C-C water circulating pump the average speed of H -- the system circulation of the head, m Ah: -- system of circulating water by A-A, head loss, pipe and boiler section C-C (3): m VA, Hi, and so can be: (2), (4) is not under pressure The lift of the circulating pump is needed when the heating system of the pressure boiler is running normally. For a heating system, the circulating pump of the atmospheric boiler heating system that does not bear the pressure of the system is not selected according to the system circulation flow and type (2), and (4) the pump head determined. Because the flow rate of the water supply to the expansion tank when the circulating pump starts is less than the system circulation volume, so the actual pump selection is only based on the lifting head determined by the type (4).
3 the calculation equation of the height and volume of the expansion tank set up in the high pressure heating system is: the formula (6) indicates that the difference between the expansion tank and the pressure relief tank should be enough to overcome the head loss of the pipe section when the system is running.
The expansion tank in addition to absorb water to swell due to the heating system of the volume, but also from the beginning of operation volume taken from the open and discharge of water within the boiler pressure float valve inside the water tank, the water tank for V expansion volume: D boiler pressure diameter, m; Ah -- fully open the pressure relief tank liquid level float valve within the required 4 conclusions 41 system should be circulation flow and pressure relief tank from the reference surface height and type (4) according to the calculation of the heating system. Choose not to bear the pressure of the system of boiler pressure pump. 42 in addition to the installation height of expansion to meet the requirements of a system of the highest point of the outer water tank, should also consider the expansion tube access point to the water capacity of the pressure relief pipe between the water tank, in order to reduce the installation height of expansion tank, expansion pipe access point should be close to the pressure relief tank or the increase of C-C to A-A section of pipe diameter.
When the water capacity of the 43C-C to A-A section pipe is large or the expansion tank is too high, the floating ball valve in the pressure relief tank is closed during the system operation.
44, the volume of the expansion tank should be considered. Besides the expansion of the system, the volume of water added to the floating ball valve in the pressure relief tank should also be considered at the beginning of the circulating pump, otherwise the system will often lose water.
45 the engineering design example shows that if the atmospheric boiler is located at the high heating system, if the design is not proper, it will cause periodic water deficit, and there is a phenomenon of system level and vertical imbalance.
46 when the pressure capacity of the normal pressure boiler is permitted, the boiler in the low position system should be used as far as possible.