The heat source is mainly coal-fired, gas-fired, oil-fired boilers or electric boilers, and geothermal, water and ground source heat pumps can also be used. The central coal-fired boiler is still the main heating source in northern China. Due to the improvement of environmental protection requirements, Beijing and other places are gradually changing the situation of coal-burning, replacing it with clean energy such as gas and electricity, and geothermal and heat pump technologies are also gradually developing.
Energy saving of heat source in boiler room is mainly to improve energy conversion efficiency, including improving the efficiency of heat exchangers in boilers and heat exchange stations, reducing the energy consumption of conveying systems, including fans and pumps, and reducing the energy consumption of auxiliary systems, including coal conveying, ash discharging and sewage discharging systems.
In the indoor heating design of buildings, there are many nonstandard artificial additions, and the calculated heat load is often far higher than the actual needs. The most direct performance is that the operating parameters of the heating system deviate from the design parameters. Common artificial additions are as follows:
(1) The heat transfer coefficient of the envelope is too large. The heat transfer coefficient of envelope calculated according to the Code for Thermal Design of Civil Buildings should be directly used as the basis for calculating the thermal load of buildings, but it is increased by 20% ~ 30% for fear that construction problems will affect the thermal insulation effect.
(2) The pipe diameter is too large. When selecting the pipe diameter, hydraulic calculation is not carried out, and the pipe diameter is only selected according to the specific friction. Each pipe diameter is large or small, and sometimes it is intentionally enlarged.
(3) The radiator area is too large. When the radiator area or quantity is selected, the calculation load will increase by 30% ~ 50%.
(4) The boiler selection is too large. In the design, there is no hydraulic calculation or even thermal load calculation, but the boiler surplus is estimated according to the area index, so that the boiler surplus is doubled.
In enterprises, large boilers, large pumps, thick pipes and large radiators are very common, and the boiler capacity is too large, which makes the boiler often stop or run at low load, affecting the thermal efficiency of the boiler. If the pipe diameter is too large and the internal resistance of the monomer is too small, it is not conducive to the hydraulic balance of the whole heating network, which will lead to uneven cold and heat in the whole heating area. Excessive heat dissipation area will cause the vertical temperature imbalance of the heating system in the building, the high-rise building will be overheated, and the bottom floor will be cold, which will not meet the comfort requirements and cause energy waste. The large pipe diameter and large heat dissipation area also create conditions for the unreasonable operation of the heating system with "large flow and small temperature difference", which increases the power consumption of the circulating water pump and the operating cost of the system. These additions also cover up the problems existing in building envelope construction and equipment installation, which seriously hinders the improvement of heating design level, increases engineering investment and wastes energy.
In order to improve the old heating system, boilers, heat exchangers, circulating pumps and other equipment should be inspected comprehensively, and the rationality of all equipment matching should be analyzed. Then, according to the actual situation, the best allowable scheme is formulated in the cold period and the early cold period, so as to increase the primary water temperature and reduce the number of boilers, heat exchangers and pumps to save energy. For the newly-built heating system, it is necessary to determine the heat load, select equipment and adopt frequency conversion speed regulation technology according to the energy-saving design standard, and try to raise the primary water temperature during operation to avoid energy waste.
Implementation method of boiler transformation
The technical transformation of industrial boilers is a systematic project, which needs to take into account various laws and requirements such as energy saving, safety and environmental protection. Moreover, the boiler unit is power equipment, which requires high reliability. If the impact and loss caused by improper transformation far exceed the scope and value of the unit itself, certain working procedures must be followed.
(1) Thermal test before reconstruction (conclusive test). Through the test, the actual situation of the boiler is fully understood, and the data of thermal efficiency and various heat losses are obtained.
(2) Analyze the main problems. According to the test data, supplemented by on-site inspection of boilers and auxiliary machines, and after listening to the opinions or suggestions of operators and maintenance personnel, comprehensive analysis and research are carried out to find out the main problems and key parts of boilers with low efficiency or reliability and low availability.
(3) Formulate the transformation scheme and put forward the feasibility study report. According to the main problems found, the energy-saving potential is analyzed, and the practical and feasible transformation scheme is selected according to the principle of technical reliability. The preliminary scheme is analyzed in detail in terms of technology and economy, and its economic feasibility is confirmed, and a feasibility study report is put forward.
The feasibility study report shall at least include the following contents:
The present situation of boiler units, including heat load, coal consumption, thermal efficiency, existing problems, etc.
The necessity of transformation;
Selection of transformation scheme (including scheme comparison);
Investment estimation of recommended scheme;
Sources of funds;
Energy saving benefits;
Environmental benefits;
Economic benefit analysis;
Sensitivity analysis;
Conclusion.
(4) Project financing. According to the feasibility study report, put forward investment estimation, determine the amount of self-raised funds and loan application subsidies, and carry out financing.
(5) Select the implementer. After the scheme is selected, the unit with good reputation, good performance and reasonable price is selected from the technology owners as the implementer.
(6) Go through the examination and approval procedures for boiler renovation. Generally, the transformation work should be submitted for approval to the following units: the superior competent department, the competent department of energy conservation and environmental protection, and the competent department of labor safety.
(7) Complete the construction design and organize the construction. The construction process shall be supervised by the special equipment testing center.
(8) Confirmatory thermal balance test. After the boiler transformation is completed, the heat balance test should be carried out under normal debugging conditions. In general, both positive and negative balance tests should be carried out. For large industrial boilers, only unconditional negative balance test can verify the transformation effect.
The verification of transformation effect depends not only on the improvement of thermal efficiency, but also on the comparison of data changes of main problems in boiler diagnosis and test, so as to judge which technical measures are effective and which are ineffective, and provide valuable practical experience for making transformation plans in the future.
In addition to urban cogeneration central heating and boiler room centralized or separate heating sources with different fuels, gas-fired wall-hung boiler heating and direct electric heating have been developed recently. Gas-fired wall-hung boiler has the advantages of convenient use and adjustment, high energy efficiency, convenient metering and charging, saving investment in heating network, and no need to occupy boiler room, but there are some problems such as gas safety, fire fighting, environmental pollution caused by exhaust gas, high user cost and short depreciation period of equipment. Direct electric heating can use low-temperature radiation electric heating film, cable buried underground, electric heating, etc. It is characterized by no external facilities, less investment, no local pollution, convenient metering and charging, and convenient management, but the energy utilization rate is too low and the operating cost is high, so this method can only be applied when other heating methods are difficult to use.
Energy saving of heating network in heating system
The heating network that transports heat energy from heat sources to users should also strive to reduce energy loss. Therefore, pipeline insulation must be done well to meet the requirements of insulation standards; It is necessary to balance the pipe network to avoid heat loss caused by different distances between heat users and heat sources; It is also necessary to prevent the pipe network from running, leaking, dripping and leaking, especially the problem of a large amount of water loss.