The first high-cold high-altitude pressure hot water boiler heating demonstration project was put into operation
As one of the first demonstration projects for heating in high-altitude and high-altitude areas in China, Qinghai-Tibet Railway Co., Ltd. has purchased three natural gas boilers from Delingha Railway Station and Lhasa Railway Station to achieve heating along May 2016. District heating demonstration projects have achieved initial results.
Lhasa is located on a snowy plateau with an altitude of more than 3,600 meters. The alpine grassland climate divides the year into two seasons, cold and warm, and the winter is long and severe. The so-called summer is only a short heating time. Our company is located on a snowy plateau in Lhasa. In winter, the temperature difference between day and night is large, the altitude is high, the air is thin, the air pressure is low, and the oxygen content is low, which affects the combustion conditions and heat load of gas heating hot water boilers. Adapting to the local climate, the current energy-saving technology and energy-saving points of Lhasa heating boilers in high-altitude areas have been designed, produced, and operated, and have won high praise from users.
With the continuous improvement of people's living standards in China, urban heating and environmental pollution factors have become a basic and indispensable important people's livelihood project related to the safety of the general residents.
In order to eliminate the impact of local climate and environment on gas heating water heaters, a more economical and reasonable solution is proposed to provide safe and qualified products for the majority of Tibetan families.
Then, in the high altitude area, which is located on a snowy plateau, the temperature difference between day and night in winter is high, the air is thin, the air pressure is low, and the oxygen content is low, which has a great impact on the combustion conditions and heat load of gas heating hot water boilers. What precautions do we need when choosing a gas-fired hot water boiler?
The high-altitude area is mainly taken as an example of the Lhasa region in Tibet. The main features of the climate of Lhasa in Tibet are as follows.
Main climate characteristics of Lhasa, Tibet
1 Influence of high altitude areas on gas heating water heaters
Before explaining the solution, we will briefly introduce the basic principles of gas heating water heaters. At present, the products on the market are divided according to output power, mainly 18kW, 24kW, 28kW, 32kW, 36kW; according to the use function, there are heating and bathroom dual functions, single heating, single heating with water storage tanks, etc .; the structure of the whole machine is mainly divided into For waterway system, combustion system, smoke exhaust system, control system, etc., as shown in Figure 1. Therefore, to solve the impact of high altitude on gas heating water heaters, it is mainly to improve the above internal structures.
1.1 Effect of altitude on heat load of gas heating water heater
Altitude and atmospheric pressure affect the heat load of gas heating water heaters. Taking Guangzhou as an example, when the gas heating water heaters commissioned are installed in Lhasa and used, the heat load will be relatively small. According to GB25034-2010, the relationship between the corresponding altitude and the heat load of gas heating water heaters can be obtained.
In order to solve the problem that the products debugged in the plain area can be used in high altitude areas (Lhasa), we can eliminate the problem of altitude by increasing the pressure in front of the nozzle or increasing the nozzle aperture, or even increasing the fire exhaust of the burner to increase the gas flow. The effect of heating load on heating water heaters.
According to the design calculation, the following gas flow parameters can be obtained, which are compared between Shaanxi and Lhasa. Therefore, when the product is debugged before leaving the factory, the input power of the product must be converted to the local power parameters of Shaanxi for factory debugging.
1.2 Influence of Altitude on Combustion System in Gas-fired Heating Furnace
Most of the gas heating water heaters use atmospheric gas combustion systems, and the excess air coefficient required for combustion is generally 1.3 to 1.8. Too much excess air results in reduced thermal efficiency, and too little air causes insufficient combustion. The higher the altitude is, the less the oxygen content is, and the high-altitude winter and spring oxygen content are also different. Too little excess air will affect the flue gas index and combustion conditions of the combustion system. The performance mainly includes the following aspects:
1) In the case of insufficient oxygen, the flue gas index becomes worse, such as increased CO and NOX;
2) In the case of insufficient oxygen, the stability of the flame is affected, that is, the height of the flame becomes longer, which will seriously cause the outer flame of the flame to burn to the main heat exchanger;
3) In the case of insufficient oxygen, the combustion is insufficient, and the fins of the main heat exchanger are liable to generate carbon particles, which affects the service life of the heat exchanger and blocks the flue gas passage.
We designed the following solutions to effectively improve the impact on the combustion system in the absence of oxygen:
Reducing the flow velocity of the fire exhaust outlet surface of the burner and increasing the number of fire exhausts can effectively solve the problems such as the phenomenon of misfire during combustion and the length of the flame height. The combustion of the gas is more sufficient, and the pressure behind the valve is not too high.
The surface of the fire outlet of the A burner was changed from a slotted hole to a round hole and a slotted shape, which is more suitable for the lack of oxygen in plateau areas.
1.3 Increase the exhaust of the fan to provide adequate oxygen combustion
Most gas heating water heaters use forced exhaust. The role of the fan in the gas heating water heater is to force the exhaust gas to the outside, and at the same time make the closed combustion system generate negative pressure. The outdoor air is sucked in through the balanced flue. The combustion chamber satisfies the combustion needs, and the gas is fully burned. From Table 1, it can be seen that the oxygen content on the plateau (Lhasa region) is only about 64.3% in the plain region, which mainly has the following two effects:
First, on the plateau, in order to ensure the full combustion of the gas in the gas heating water heater, the fan air volume Q must be increased, which can be increased by increasing the fan power and turbine;
Second, the influence of the operating parameters of the wind pressure differential switch.
The main functions of the wind pressure differential switch are used to detect the smoothness of the smoke pipe, shut down the equipment before the smoke exceeds the standard (that is, the CO concentration is greater than 0.1%), and the operation of the fan. The principle uses the theory in fluid mechanics to design a venturi tube to collect negative pressure, and collect pressure parameters of negative pressure in the exhaust pipe or air chamber, respectively. Because the collected air pressure is affected by the air pressure environment, such as atmospheric pressure and ambient temperature. The wind pressure switch is a protective component of the combustion system. It plays a key role in ensuring the safety of combustion, so its action must be accurate.
1.4 Influence of High Altitude on Heating Water Circulation System
In gas-fired heating water heaters, the function of the heating water circuit circulation system is to heat the heating water and circulate it in the heating system. Its core component is the circulating water pump, which is used to provide circulating power for hot water in the heating system. In Lhasa, Tibet, the temperature rise of the pump motor and the commutation of the pump motor are adversely affected. Therefore, the pump power in the water system must be designed to meet the water resistance lift that needs to be overcome.
1) High altitude, the greater the temperature rise of the pump motor, the lower the output power;
2) Corona-proof measures should be taken when high-voltage motors are used in plateaus.
For the development of suitable gas heating hot water boilers in high altitude areas, adjustments need to be made from the entire combustion system, smoke exhaust system and heating water circulation system; otherwise, problems such as flashback, excessive smoke, and substandard heat load will occur to consumers. Bring impacts, and even security risks. Through the above adjustments for high-altitude gas heating water heaters, the adverse effects of high altitudes can be eliminated.