With the advent of winter, industry relies even more on a reliable heating system to ensure smooth production operations during the cold season. And in this warming system, industrial atmospheric hot water boiler heating system undoubtedly plays a key role. However, as the heating season approaches, we must also face a number of challenges that can affect the normal operation of the heating system.

Just as every machine needs regular inspection and maintenance, atmospheric hot water boilers also need our attention and care. Let's discuss some common problems that may be encountered in industrial atmospheric hot water boiler heating system and the corresponding solutions to ensure that in this cold season, industrial production can continue to run efficiently and smoothly.

Atmospheric pressure hot water boiler is the boiler body open or through the vent pipe with the atmosphere, in any case, the boiler body top gauge pressure is zero. In the design and installation of atmospheric pressure hot water boiler project, the system often appears in the pipe network leakage and corrosion, through the large gas pipe overflow, boiler common vent pipe between the water cycle and other problems.

Design of water system for atmospheric hot water boiler

According to whether the boiler water is directly involved in the circulation of the end heating system, it can be divided into inter-supply and direct-supply systems.

1. Inter-supply systems

Atmospheric hot water boiler inter-supply system is a more common form of system, the boiler room is set up in the high expansion tank, in order not to make the water in the pot-barrel local vaporization, when the rated water supply temperature is not higher than 85 ° C, the general design to ensure that the lowest level of the high level tank than the highest point of the primary circulating system 1.0 ~ 1.5 m high, while ensuring that the system does not vaporize, not emptying. The system pressure point is set at the suction end of the circulating water pump, and the circulating water pump is set at the discharge end of the boiler to ensure that the boiler operates at atmospheric pressure.

2. Direct supply system

Atmospheric hot water boiler direct supply system is divided into single-point pressure-setting system and double-point pressure-setting system 2 kinds of single-point pressure-setting system only in the boiler room to set up the expansion tank, the system pressure-setting point is set at the suction end of the circulating pump double-point pressure-setting system in the system at the highest point and then set up a high-level expansion tank. Atmospheric hot water boiler direct supply system is through the circulating pump to overcome the system's circulating flow resistance and expansion tank level and the highest point of the system of the height difference, so that the system operates normally.

Normal pressure hot water boiler usage scenarios

According to the characteristics of the inter-supply system and direct-supply system, in general, when the heating system end of the form of more, the need for a variety of water supply temperature, or building height, high and low district heating, it is recommended to use the inter-supply system; when the end of the form of a single heating, and the height of the building is relatively low, it can be used to use the direct-supply system, the use of direct-supply system, should be considered due to the circulating pumps to overcome the height difference of the system and the increase in energy consumption.

In the atmospheric hot water boiler project design practice, if you simply use the above system form, do not take into account the different conditions of each boiler room itself, especially in the limitations of the project space conditions, the construction of the level of difference and the level of operation of the objective factors such as high and low level of generalization of the design, the system put into operation is likely to be a problem.

Problems encountered in the project and their solutions

1. Deficiencies and Improvements in Pressure Setting for Direct Supply Systems

A district boiler room with atmospheric hot water boiler, heating area of about 50,000m² , heating system for a single point of fixed-pressure direct supply system. The system was put into operation for 1 year, found that there are two problems: 1) non-heating season air into the system, the pipe network is prone to corrosion; 2) circulating water pump in the stop-start pump or cut pump, the boiler room of the main return pipe water hammer phenomenon, start/stop valve is very easy to be damaged.

To address issue #1, the preliminary program discussion considered changing to a two-point constant pressure system, which could accommodate wet maintenance after system shutdown.

A constant-pressure make-up water pump is installed in the boiler room, with the location of the pressure setting point taken on the end side before the start/stop valve. The make-up pump is used only during the non-heating season when the furnace system is shut down for wet maintenance; before the circulating pumps are put into operation during the heating season, the make-up pump stops running and is isolated from the system by means of a check valve, preventing the instability of the system's pressure setting.

To solve the 2nd problem, a bypass pipe and check valve are added to the heat load side of the start/stop valve and the check valve at the outlet end of the circulating water pump. Circulating water pump operation, the check valve is closed, the hot water system normal circulation; circulating water pump pump stops pumping, the opening and closing valve quickly closed, and the opening and closing valve has a high position head, through the bypass pipe drive water flow to the water supply pipe, the formation of the cycle, due to the pipeline resistance gradually eliminates the potential energy of the position head, to avoid the rapid closure of the valve to avoid the rapid closure of the phenomenon of water hammer.

2. Problems and solutions of water overflow from the vent pipe to the expansion tank

The boiler room of a neighborhood is equipped with atmospheric hot water boilers, heating an area of about 200,000m² , and the system is an inter-supply system. After the heating test run, it was found that the vent pipe was overflowing to the expansion tank, resulting in loss of energy and heat.

In order to solve this problem, the preliminary consideration is to adjust the location of the fixed pressure point to solve the problem, that is, the atmospheric hot water boiler vent pipe directly to the bottom of the expansion tank. By increasing the height difference between the upturned level of the vent pipe and the level of the expansion tank, run again, the overflow problem is solved.

3. Problems and solutions of multiple atmospheric hot water boilers sharing common vent pipes

A hot water boiler room with a heating area of approximately 120,000 m² uses five pressurized hot water boilers, which were changed to an atmospheric system in a 2017 low-NOx retrofit, with the practice of each boiler vent stub converging to the main vent pipe, which then flips up to the expansion tank.

After the system was put into operation, it was noticed that the boiler's vent pipe was very hot, and there was flow through the vent pipe as measured by a portable flowmeter, with small circulations occurring between each boiler's vent stubs.

Therefore, the comprehensive solution to the case problem is as follows:

1) Reduce the head difference of the pressure measuring tubes between boilers. Minimize the specific friction of the supply and return mains as far as technically and economically reasonable;Increase the branching design in the way boilers are connected to each other so that the number of boilers on each branch is as equal as possible; try to use boilers of the same brand and with the same output.

2) If the boiler room has more space, design separate vent pipes for each boiler to completely eliminate the path of water flow between each boiler.

3) Boiler room water system commissioning is completed, each boiler vent pipe connection point pressure measurement pipe head may not be exactly the same, the vent pipe can be insulated to reduce the heat loss of the system.

Conclusion

In the design of the atmospheric hot water boiler system, the following measures can be taken to avoid corrosion of the pipe network, water hammer, vent pipe overflow and water flow.

1) atmospheric hot water boiler direct supply system can be set up fixed-pressure make-up water pump, the make-up water pump is only used in the non-heating season when the system is wet maintenance, in order to reduce the corrosion of the pipeline; in the opening and closing valves and circulating water pump outlet end check valve on the side of the heat load to increase the connecting pipe and check valves, circulating water pump out of service, you can avoid the phenomenon of water hammer.

2) to prevent the vent pipe to the expansion tank overflow, the design should be strictly calculated vent pipe upturned horizontal section and the height of the expansion tank level; or in the case of avoiding vapor corrosion of the circulating water pump, the vent pipe connected to the bottom of the expansion tank, fixed-pressure make-up pipe and the vent pipe together.

3) more than one atmospheric hot water boilers connected in parallel to the water system design as much as possible to make the boiler independent design of the vent pipe; such as unconditional design, the boiler should be optimized connection, try to make the boiler vent pipe connected to the water pressure is the same, to reduce the phenomenon of water flow in the vent pipe; in order to reduce the heat loss, can be insulated vent pipe treatment.