Phase-change boiler

Whether in terms of working principle or the requirements for manufacturing, installation, and operation, phase-change boilers differ significantly from conventional pressure-bearing boilers and atmospheric-pressure boilers. Existing boiler technical standards, regulations, and codes cannot be fully applied to phase-change boilers. Therefore, in line with the principles of practicality and feasibility, this standard has been formulated to establish technical requirements for the design, manufacturing, installation, and operation of phase-change boilers.

A phase change boiler is a type of boiler in which, in the boiler chamber and in the absence of non-condensable gases, the heat absorbed from flames and flue gas is continuously transferred to the heating medium inside the phase change heat exchanger through a continuous vapor-liquid phase cycle of evaporation and condensation.

Phase-change boilers are divided into steam phase-change boilers and hot water phase-change boilers, and they include vacuum phase-change boilers, low-pressure phase-change boilers, and pressure phase-change boilers.

\"Phase-change boilers\" are applicable to industrial boilers that operate through phase-change heat transfer, namely phase-change hot water boilers and phase-change steam boilers with a rated operating pressure of not more than 2.5 MPa.

　Built-in quick-install phase change boiler: A phase change heat exchanger is located within the boiler drum, resulting in a phase change boiler that is integrated with the main body of the boiler. Also known as a built-in phase-change boiler. :P :P External split-type phase change boiler: a phase change boiler in which the phase change heat exchanger is located within a dedicated heat exchanger housing outside the boiler drum (shell). Also known as an external phase-change boiler.

A dual-phase change boiler, also known as a condensing phase change boiler, possesses all the advantages of gas-phase change boilers, such as being non-explosive, free from scaling and corrosion, free from cracks and bulges, as well as ensuring safe, reliable and stable operation. In addition, it boasts the efficiency, energy savings and environmental friendliness characteristics of condensing gas boilers. By using the lower heating value as the basis for calculations in boiler thermodynamics, the thermal efficiency of such boilers can reach or even exceed 100%, resulting in particularly significant energy-saving effects. :victory:

Download of the standards for «Phase-Change Boilers»: http://bbs.hcbbs.com/viewthread.php?tid=278027&highlight=gb%2B21434

“The thermal efficiency of this type of boiler can reach or even exceed 100%? Come on! Energy conservation is already great enough – how can there be an excess?

In boiler thermal calculations, the lower heating value is used as the basis for the calculations

The boiler is designed with an ultra-low flue gas temperature, resulting in a thermal efficiency that is 2% to 3% higher than that of conventional boilers as specified in JB/T 10094-2002. A flue gas condenser is installed at the rear to reduce the flue gas temperature below the dew point temperature of water vapor, thereby recovering the heat contained in the condensed flue gas and offsetting the loss of latent heat. This allows the thermal efficiency to increase by 10% to 15%, which is 8% to 12% higher than the thermal efficiency of conventional boilers specified in JB/T 10094-2002, yielding a very significant energy-saving effect

On the 11th floor, I wonder if you have read the book \"Che De Fu. Condensing Boilers and Their Systems [M]. Beijing: Machinery Industry Press, 2002, p. 6.\" It contains some information on this topic

　Vertical shell type phase change boiler: A phase change boiler whose boiler shell axis is perpendicular to the ground. 　Horizontal shell type phase change boiler: a shell type phase change boiler whose axis is parallel to the ground. 　Horizontal drum water tube phase change boiler: a water tube type phase change boiler whose drum axis is parallel to the ground.

△ △ △ × △ × △ ××－××/××/××－××－△△ Code for fuel type; Rated operating pressure of the phase-change boiler (MPa); Maximum heat absorption capacity of the heating medium in the boiler – rated outlet/inlet temperature of the coil group (°C); Rated outlet gauge pressure for producing steam or hot water in the coil group with the highest heat absorption capacity (MPa); Rated evaporation rate of the steam boiler (t/h) or rated thermal power of the hot water boiler (MW); Code for the type of combustion equipment or combustion method; Number of drum units in horizontal water-tube boilers; Code for the basic structure of the boiler body; Number of coil groups; Code for the arrangement pattern of the coils; Code for the medium inside the boiler; Code for the type of phase-change boiler

Manufacturers of phase-change boilers shall meet the corresponding requirements in accordance with relevant regulations. Units that produce vacuum phase-change boilers must obtain a \"Boiler Manufacturing License\" issued by the provincial quality and technical supervision authority. Units that produce low-pressure phase-change boilers must obtain a \"Boiler Manufacturing License\" of grade D or higher (including grade D) issued by a quality and technical supervision authority at or above the provincial level. Units that produce pressure phase-change boilers must obtain a \"Boiler Manufacturing License\" of grade C or higher (including grade C) issued by the relevant quality and technical supervision authority.

:Lol, I had the same opinion as 11L when I was first learning about boilers. I suggest you look into the concepts of lower and higher calorific values. The calculated thermal efficiency of boilers is based on their lower heating value; as a result, the thermal efficiency of some boilers can even reach 105%.

The energy released upon the complete combustion of 1 kg of solid (liquid) fuel or 1 m3 of gaseous fuel is referred to as the calorific heat or heat value of the fuel. Considering the state of water in the fuel combustion products, the calorific value that includes the latent heat of vaporization of water is referred to as the high heat value or high calorific value (HHV) ； The calorific value that does not include the latent heat of vaporization of water vapor is called the low heat value or lower heating value (LHV)

1. Phase change within the boiler: The fluid in the lower half of the gas-phase change boiler’s interior absorbs heat from the furnace and flue tubes, causing it to vaporize and generate steam. This steam rises to the upper part of the boiler drum, where it transfers its latent heat to the fluid flowing within the heat exchange tubes. Once again, the steam turns back into condensed water and returns to the lower part of the boiler, thus creating a continuous cycle of phase change and heat transfer, which keeps the fluid in the heat exchange tubes heated continuously. The main unit is essentially a large heat pipe; the entire heating surface of the boiler functions as the heating section of the heat pipe, while the phase-change heating section in the upper part of the boiler acts as the condensing section of the heat pipe. The medium inside the boiler is in a closed space, and heat transfer takes place through liquid-vapor-liquid phase changes. 2. External phase change: After the fuel burns in the furnace inside the boiler, the smoke generated undergoes some heat exchange with the medium inside the boiler as it flows through the smoke pipes there. Nevertheless, this smoke still has a high temperature, and the water vapor in it is in a superheated state. When this smoke enters the smoke vapor condenser, it exchanges heat with the condenser, causing the water vapor to drop below its dew point temperature; as a result, most of the water vapor condenses into liquid water, undergoing a phase change and releasing latent heat of vaporization. The heat exchange of flue gas in the flue gas condenser consists of two parts: sensible heat exchange by convection and latent heat exchange by condensation. By condensing the water vapor in the flue gas, the flue gas condenser absorbs not only the sensible heat released due to the decrease in flue gas temperature, but also the latent heat released by the water vapor in the flue gas as a result of phase change. The high calorific value of natural gas, Qgr,v,ar, is generally around 36,000 to 40,000 kJ/m3. The heat that must be carried away by the water vapor produced upon burning 1 m3 of natural gas accounts for more than 10% of Qgr,v,ar, approximately 4,000 kJ. Taking the natural gas from northern Shaanxi as an example, its high calorific value is Qgr,v,ar = 37.16 MJ/Nm3, while its low calorific value is Qnet,v,ar = 33.24 MJ/Nm3. The difference between the two is ΔQ = 3.92 MJ/Nm3; this amount of heat corresponds to 3.92/33.24×100% = 11.79% of the low calorific value. For every 10% of water that is condensed, the thermal efficiency of the boiler can increase by approximately 1.2%. Recovering this amount of heat through the flue gas condenser **improves the thermal efficiency of the boiler.

I still don’t quite understand; does that mean energy is not conserved? I’m a beginner and would appreciate some guidance. When the pressure decreases, the boiling point drops, and the steam produced then condenses into water in the smoke vapor condenser, right? Is this thermal efficiency based on calculations or on the energy of nature? If calculated based on the lower calorific value, is this thermal efficiency meant for such calculations? If it is in relation to the energy of nature, then apart from the energy derived from burning materials, what else can contribute to this thermal efficiency? In a phase-change boiler, the water does not participate in the system circulation; therefore, there is no wear and tear on it, and no energy is lost either.

The flue gas exhaust temperature of gas boilers is influenced by traditional design concepts. To prevent low-temperature corrosion on the heat-exchanging surfaces at the rear of the flue gas stream due to the condensation of water vapor in the flue gas, the designed exhaust temperatures range from 150 to 250 °C, keeping the water vapor in the flue gas in a superheated state. Such high exhaust temperatures prevent the water vapor from condensing, resulting in significant losses of sensible and latent heat. 80% to 85% of the high calorific value of the fuel in conventional gas boilers is transferred to the working fluid, while the remainder is primarily lost to the atmosphere through flue gases. The heat loss carried away by water vapor in the flue gas accounts for 55% to 75% of the total heat loss from the exhaust gases. When natural gas is used as fuel, the proportion of water vapor in the flue gases after combustion is much higher than when coal is used, with its volume share reaching 15%–19%. The more water vapor present in the flue gas, the more latent heat can be utilized, and lowering the flue gas temperature results in a higher thermal efficiency. It is estimated that for every 10 °C decrease in the exhaust temperature of gas boilers, the thermal efficiency can increase by 0.43%. For gas boilers, reducing the flue gas temperature and recovering the sensible heat of the flue gas as well as the latent heat of vaporization of the water vapor in it, and making full use of them, is key to saving energy and reducing consumption. After the fuel burns in the furnace inside the boiler, the smoke generated undergoes some heat exchange with the medium inside the boiler as it flows through the smoke pipes, but it still retains a high temperature; the water vapor in the smoke is still in a superheated state. When this smoke enters the smoke vapor condenser, it exchanges heat with the condenser, causing the water vapor in the smoke to drop below its dew point temperature. As a result, most of the water vapor condenses into liquid water, undergoing a phase change and releasing latent heat of vaporization. The heat exchange of flue gas in the flue gas condenser consists of two parts: sensible heat exchange by convection and latent heat exchange by condensation. By condensing the water vapor in the flue gas, the flue gas condenser absorbs not only the sensible heat released due to the decrease in flue gas temperature, but also the latent heat released by the water vapor in the flue gas as a result of phase change. The high calorific value of natural gas, Qgr,v,ar, is generally around 36,000 to 40,000 kJ/m3. The heat that must be carried away by the water vapor produced upon burning 1 m3 of natural gas accounts for more than 10% of Qgr,v,ar, approximately 4,000 kJ. Taking the natural gas from northern Shaanxi as an example, its high calorific value is Qgr,v,ar=37.16 MJ/Nm3, while its low calorific value is Qnet,v,ar=33.24 MJ/Nm3. The difference between these two values is ΔQ=3.92 MJ/Nm3. This amount of heat corresponds to 3.92/33.24×100% = 11.79% of the low calorific value. For every 10% of water that is condensed, the thermal efficiency of the boiler can increase by about 1.2%. By recovering this heat using a flue gas condenser, the thermal efficiency of the boiler is improved.

A 2.8MW gas dual-phase change boiler, when fueled by natural gas with a lower heating value of 32660 KJ/m3, has an average output of 2.8MW for the main boiler unit, 0.30MW for the flue gas condenser, and 3.1MW for the dual-phase change boiler as a whole； The average thermal efficiency of the boiler unit is 91.35%, the average additional thermal efficiency of the flue gas condenser is 10.45%, and the average thermal efficiency of the two-phase change boiler is 101.80%. During the 5-month heating season each year, the boilers operate for an average of 8 hours per day. The cost of natural gas is 1.5 yuan per cubic meter. Assuming that a phase-change boiler with a capacity of 0.7 MW/h consumes around 75 m3 of gas, a 2.8 MW dual-phase-change gas boiler can save the following amount of fuel over one heating season: 75÷0.7×0.30×8×30×5 = 38,571 (m3). The corresponding cost savings amount to 1.5×38,571 = 57,900 yuan