CN104727976A - Combustion heating system for Stirling engine - Google Patents

Abstract

The invention relates to a combustion heating system of a Stirling engine, which is composed of a straight gradient stacked porous medium burner and a filled porous medium heater arranged up and down. The straight gradient stacked porous medium burner includes a shell, and The gas inlet, premixing chamber, axial heat insulation layer, igniter lead protection tube, igniter, gradient ceramic porous medium layer, catalytic layer, and the filled porous medium heater are arranged in the shell from top to bottom. The outer insulation layer, the metal mesh cylinder arranged in the insulation layer, and the heating pipes arranged symmetrically in the center of the metal mesh cylinder, and the gaps of the heating pipes are filled with metal wires. The invention has the advantages of stable combustion, high combustion efficiency, good heat transfer performance, good heat storage performance, stable operation, wide load adjustment range, easy adjustment, less pollution discharge, etc., and has a significant effect on improving the working efficiency of the gas type Stirling engine.

Description

Combustion heating system of a Stirling engine

technical field

The invention belongs to a combustion and heat exchange device, in particular to a combustion heating system of a Stirling engine.

Background technique

The Stirling engine is a closed external combustion engine, which has the advantages of wide fuel sources, high thermal efficiency, less exhaust pollution, good operating characteristics, low noise, etc., and is widely used in the fields of distributed energy, clean gas power generation and solar power generation It has important applications and has attracted more and more attention.

The external combustion system is an important part of the Stirling engine. Its main function is to convert the chemical energy of the fuel into thermal energy through a reasonable and efficient organization of combustion and heat exchange, and transfer it to the heater through the heat exchanger, and then the heater The heat energy is transferred to the working medium in the machine through heat exchange, so that the working medium in the machine expands and does work in the engine, and converts heat energy into mechanical energy. It can be seen that the efficiency of an engine not only depends on the cycle efficiency of the engine itself, but also has a great relationship with the combustion conversion efficiency of its external combustion system. Therefore, to design an efficient and reliable Stirling engine, the design of the external combustion system is very important.

The working fluid inside the Stirling heater is in a pressurized state, and its density is relatively high; the flow rate is also relatively high, so the internal heat exchange is sufficient. The density of the external combustion products is small and the flow rate is low, so that the necessary heat transfer can only be transferred by a large temperature difference. Therefore, improving the heat transfer effect outside the heater tube will greatly improve the working performance of the heater. At the same time, uneven heating often occurs in many heater parts, that is, "hot spots". In order to prevent the heating tube from being burned, the "hot spot" temperature must be equal to or lower than the maximum operating temperature (metallurgical limit) that the metal can withstand. In fact, the average temperature of the heater part is much lower than the metallurgical limit (can be as low as 100 ℃), and such a low average temperature will reduce the power and efficiency of the engine at the same time.

In summary, in order to improve the working performance of the Stirling machine, it is necessary to optimize the design of its combustion chamber and heater. Therefore, the present invention designs a combustion heating system for a gas-type Stirling engine by adopting porous combustion heat exchange technology. Make full use of the good heat storage capacity, intense disturbance, strong heat conduction and radiation capacity of porous media, so that the temperature in the combustion chamber is more uniform, and the average temperature reaching the heater surface is high, thereby improving the power and efficiency of the engine. The system can be applied to a gas-type Stirling engine, especially a gas-type Stirling engine working in a distributed energy station and mainly operating in a stable working condition.

Related Stirling devices are also disclosed in the prior art. For example, Zhang Baosheng, Gong Xiaomao and Zhou Fan of China University of Mining and Technology invented a thermal storage coalbed methane Stirling device, patent number: 201120056598.8. This utility model utilizes the high-temperature flue gas produced by the porous medium burner to achieve high-efficiency transfer of heat through the coil pipe coiled in the heat storage. Realize the power generation of unstable coalbed methane, especially low-concentration coalbed methane, effectively reduce the impact of unstable coalbed methane gas sources, especially large concentration fluctuations, on the entire device, and at the same time have high thermal efficiency, low pollution, low noise, convenient movement, and easy maintenance, etc. advantage. However, the structure of the porous media burner is too simple, which is prone to combustion instability. At the same time, the design of the heat head is simple, which also limits the heat transfer performance.

Cen Kefa and Cheng Leming from Zhejiang University designed a utility model for a gradual change porous media burner, patent number: 01226080.0. It has a burner shell and its insulation layer, a secondary air distribution ring is provided on the inner wall of the burner shell and its insulation layer, and a heat dissipation ring, a premixing chamber, a gas inlet and The air inlet is equipped with a mixed gas uniform distributor in the center of the radiator, and a non-uniform porous medium with a gradient void ratio is installed in the secondary air distribution ring. The gradually changing porous media burner has the advantages of stable combustion, high combustion efficiency, low NOx emission, and low pollutant emission, small volume, compact structure, wide load adjustment range, and obvious economic efficiency. But because this invention is mainly used for research experiments, in order not to change the structure of the porous medium layer inside the burner, it is selected to use electric spark ignition at the outlet of the combustion chamber. This design is not conducive to the application on the Stirling machine, and makes the burner The ignition time is greatly increased.

Contents of the invention

The object of the present invention is to provide a combustion heating system with high combustion efficiency, good heat transfer performance and low pollution emission, which can be used by a Stirling engine in order to overcome the above-mentioned defects in the prior art.

The purpose of the present invention can be achieved through the following technical solutions:

A combustion heating system of a Stirling engine, which is composed of a straight gradient stacked porous medium burner and a filled porous medium heater arranged up and down,

The straight gradient stacked porous media burner includes a casing, and a gas inlet, a premixing chamber, an axial heat insulation layer, an igniter lead wire protection tube, an igniter, Gradient ceramic porous medium layer, catalytic layer,

The filled porous medium heater consists of an external insulation layer, a metal mesh cylinder arranged in the insulation layer, and heating tubes arranged symmetrically in the center of the metal mesh cylinder, and metal wires are filled in the gaps of the heating tubes.

The pre-mixing chamber is filled with filamentous porous medium material, on the one hand, it can form a turbulent flow to make the gas and the preheating air mix well, on the other hand, it can prevent the gas from being tempered or the temperature of the preheating air is too high, etc. The reason is that the temperature of the premixed gas exceeds the ignition point of the gas, causing the premixed chamber to explode. When the temperature of the local space in the premixing chamber is too high due to some factors to cause a sudden fire, the porous media material with a lower temperature around it can quickly absorb the heat of combustion, so that the loss of combustion heat is greater than the reaction heat generated by combustion; at the same time, the analysis of the chain The reaction mechanism shows that due to the contact with the chaotic porous media material, some active groups (free radicals) in the flame lose their activity and are destroyed, so that the chain free radical reaction is terminated, resulting in gap flame suppression, and the premix chamber will not explode. Danger.

The shell is a double-layer structure composed of an inner shell and an outer shell. The inner shell is made of high temperature resistant corundum material. The outer shell includes an inner layer of thermal insulation material and an outer layer of structural steel material. Between the inner shell and the outer shell Leave air to preheat the interlayer.

An air inlet is arranged below the housing, and fresh air is blown into the air preheating interlayer by an external blower from the air inlet to form preheating air, and at the same time, the inner housing can be cooled to prevent its temperature from being too high.

The center of the axial heat insulation layer is a mixed gas injection hole, and preheating air passages are arranged around it.

The igniter is a conical electric heating igniter, and there is a certain free space near the igniter, which is made into a miniature blunt stable burner and placed upstream of the main combustion area. Compared with the electric spark type igniter, the electric heating type igniter ignites reliably. The conical blunt body stabilizer can form a recirculation zone at the tail of the blunt body to achieve the purpose of stabilizing the flame. Located upstream of the main combustion zone can well preheat the porous media in the combustion zone and increase the ignition rate. When the combustion is stable, the free space with poorer heat transfer than the porous medium can effectively block the heat and flame from propagating upstream, protect the igniter from being burned out and prevent the occurrence of backfire.

The gradient ceramic porous medium layer is a medium layer composed of multilayer foamed ceramics whose pore diameter gradually increases from top to bottom.

The catalytic layer is a porous media catalytic layer. On the one hand, the position is located downstream of the combustion area, and can catalyze the reaction of _NOx , CO, and HO generated during the combustion process into harmless CO ₂ , H ₂ O, and N ₂ ; On the one hand, the location is close to the combustion area, and the temperature is relatively high, which can keep the reaction speed at a high level and make the catalytic process more complete.

The center position of the metal mesh cylinder is provided with an air cyclone, and 46 inverted U-shaped heating pipes are arranged symmetrically around the center of the cyclone, and the air cyclone is used to divide the flue gas flow into eight equal-flow tangential streams in different directions. The air flow can make the air flow in all directions more uniform, and make the air flow tangentially pass through the heat exchange tube area, increase the time for the air flow to scour the heat exchange tube, and improve the heat transfer efficiency.

There is a certain thickness of free space between the metal mesh cylinder and the external insulation layer, so that the air pressure at all positions around the mesh cylinder is roughly the same, so as to ensure that the airflow in all directions in the cylinder is fully distributed and evenly distributed.

Compared with the prior art, the present invention has the following advantages:

1. Using an electric heating type igniter (conical in shape) to ignite the premixed gas at the upstream of the combustion chamber and stably burn the flame greatly reduces the start-up time of the porous media burner, and at the same time the exhausted flue gas can also be preheated Stirling machine heaters, thereby minimizing heat waste during the start-up phase of the porous media burner. And the hollowed-out porous medium at the center effectively blocks the heat and flame from spreading upstream after stable combustion, protecting the igniter from being burned out and preventing the occurrence of backfire.

2. Reduce the thermal inhomogeneity of the combustion chamber, reduce the local high temperature range and effectively reduce its temperature, thereby reducing the emission of NOx and other polluting gases.

3. Increase the average temperature of the entire combustion area, improve the combustion conditions, and the catalytic layer at the end of the combustion area further catalyzes the burnout of combustible gases. Make the combustion more complete, reduce the emission of pollutants such as CO caused by incomplete combustion; and reduce the excess air coefficient to reduce the emission of exhaust heat and improve machine efficiency.

4. By rationally arranging the flow direction of the airflow and the uniform temperature of the porous medium, the temperature distribution near the heating tube can be uniform, the thermal stress of the heating tube can be improved, the high temperature performance requirements of the heating tube for metal materials can be reduced, and cheaper materials can be used Production and processing, reducing the manufacturing cost of the Stirling machine is conducive to the commercialization of the Stirling machine.

5. Utilize the good radiation, convection, and heat conduction of porous media to increase the heat exchange effect between the heater and external flue gas, optimize the heat exchange performance of the heater, and improve the power and efficiency per unit volume of the engine combustion chamber and heater.

6. Enhance the heat storage performance of the Stirling engine heater, make it easier to maintain a stable heater temperature, and optimize various operating performances of the engine (such as easier to maintain a stable speed, adapt to relatively harsh load changes and gas instability, optimize Starting performance, etc.) improve the practicality of the Stirling machine.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is the structural representation that the present invention is applied on the Stirling engine;

Fig. 3 is a schematic diagram of the structure of the air cyclone.

In the figure, 1-gas inlet, 2-igniter lead protection tube, 3-premix chamber, 4-preheating air channel, 5-mixed gas injection hole, 6-igniter, 7-gradient ceramic porous medium layer, 8-air preheating interlayer, 9-outer shell, 10-inner shell, 11-air inlet, 12-catalytic layer, 13-metal wire, 14-heating pipe, 15-air cyclone, 16-flue gas outlet, 17 - Thermal head heating nozzle, 18 - Stirling engine, 19 - Combustion heating system.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example

A combustion heating system 19 of a Stirling engine, the structure of which is shown in Figure 1, is composed of a straight gradient stacked porous medium burner and a filled porous medium heater arranged up and down.

The straight-shaped gradient stacked porous media burner includes a shell, and a gas inlet 1, a premixing chamber 3, an axial heat insulation layer, an igniter lead wire protection tube 2, and an igniter 6 are arranged sequentially in the shell from top to bottom. , Gradient ceramic porous medium layer 7, catalytic layer 12. The filled porous medium heater consists of an external insulation layer, a metal mesh cylinder arranged in the insulation layer, and heating tubes 14 arranged symmetrically in the center of the metal mesh cylinder, and metal wires 13 are filled in the gaps of the heating tubes 14 .

Specifically, filling the pre-mixing chamber 3 with a filamentous porous medium material can form a turbulent flow on the one hand to mix the gas and preheated air well; The temperature of the hot air is too high, causing the temperature of the premixed gas to exceed the ignition point of the gas, causing the premixed chamber to explode. When the temperature of the local space in the premixing chamber is too high due to some factors to cause a sudden fire, the porous media material with a lower temperature around it can quickly absorb the heat of combustion, so that the loss of combustion heat is greater than the reaction heat generated by combustion; at the same time, the analysis of the chain The reaction mechanism shows that due to the contact with the chaotic porous media material, some active groups (free radicals) in the flame lose their activity and are destroyed, so that the chain free radical reaction is terminated, resulting in gap flame suppression, and the premix chamber will not explode. Danger.

The shell is a double-layer structure consisting of an inner shell 10 and an outer shell 9. The inner shell 10 is made of high-temperature-resistant corundum material, and the outer shell 9 includes an inner layer of thermal insulation material and an outer layer of structural steel material. Air is left between the inner shell 10 and the outer shell 9. Preheat sandwich 8. An air inlet 11 is arranged below the shell, and fresh air is blown into the air preheating interlayer 8 by an external blower from the air inlet 11 to form preheating air, and meanwhile, the inner shell 10 can also be cooled to prevent its temperature from being too high.

The center of the axial heat insulation layer is a mixed gas injection hole 5, and a preheating air passage 4 is arranged around it. The igniter 6 is a conical electric heating type igniter, leaving a certain free space near the igniter 6, making a miniature blunt body stable burner, and placing it upstream of the main combustion area. Compared with the electric spark type igniter, the electric heating type igniter ignites reliably. The conical blunt body stabilizer can form a recirculation zone at the tail of the blunt body to achieve the purpose of stabilizing the flame. Located upstream of the main combustion zone can well preheat the porous media in the combustion zone and increase the ignition rate. When the combustion is stable, the free space with poorer heat transfer than the porous medium can effectively block the heat and flame from propagating upstream, protect the igniter from being burned out and prevent the occurrence of backfire.

Gradient ceramic porous medium layer 7 is a medium layer composed of multilayer foamed ceramics whose pore diameter gradually increases from top to bottom. The catalytic layer 12 is a porous media catalytic layer. On the one hand, this position is located downstream of the combustion area, and can catalyze the reaction of _NOx , CO, and HO generated during the combustion process into harmless CO ₂ , H ₂ O, and N ₂ ; , the position is close to the combustion area, and the temperature is relatively high, which can keep the reaction speed at a high level and make the catalytic process more complete.

An airflow swirler 15 is arranged at the center of the metal mesh cylinder, the structure of which is shown in FIG. 3 . 46 inverted U-shaped heating pipes 14 are symmetrically arranged in the center around the cyclone, and the airflow swirler 15 is used to divide the flue gas flow into eight equal-flow radial airflows in different directions, which can make the airflow in all directions more uniform and make the The air flow passes through the heat exchange tube area in a radial direction, increasing the time for the air flow to scour the heat exchange tube and improving heat transfer efficiency. There is a space between the metal mesh cylinder and the external insulation layer, and the gap between the fins of the cyclone and the heating tube is filled with a porous medium heat-conducting material made of metal wire 13, so as to ensure that the airflow fully exchanging heat in all directions in the cylinder is evenly distributed. A flue gas outlet 18 is arranged under the outer insulation layer, and a heating nozzle 17 of a heating head is arranged at the bottom of the heating pipe 14 to connect to the regenerator.

This combustion heating system 19 can be applied on the Stirling engine 18, and the air enters the air preheating interlayer 8 between the inner shell 10 and the outer shell 9 of the burner through the blower at a relatively high flow rate through the air inlet 11 for preheating and cooling The inner casing 10, then enters the preheating chamber 3 on the upper part of the burner through the preheating air passage, mixes with the gas entering the premixing chamber through the gas inlet 1, and then enters the combustion chamber part through the mixed gas uniform distributor, and is heated by electric heating. After being heated and ignited, the igniter 6 enters the gradient ceramic porous medium layer 7 for combustion. Finally, it enters the heater part after being completely burned through the catalytic layer 12, and then enters the heat exchange area after being adjusted by the airflow swirler 15. It uses the good heat conduction, convection, and radiation characteristics of the metal wire porous medium to exchange heat with the heating tube and then exits the flue gas. 16 discharge.

After the hot head and the heating tube of the Stirling engine 18 absorb the heat of the high-temperature flue gas, the relative movement of the piston in the cylinder produces a volume change, pushing the medium to reciprocate in the closed cavity, and the gas is heated at a lower temperature and pressure. The working medium is compressed, and the working medium is heated and expanded under higher temperature and pressure, so as to obtain cycle work in the Stirling cycle, and cooperate with the power transmission system to output mechanical energy to the outside.

As a new combustion heating system, after theoretical analysis and practice test, it is considered that this system is feasible, and there are mainly the following aspects as the theoretical and application basis:

The main difference between the combustion heating system of the Stirling engine of the present invention and other Stirling engine combustion heating systems is that its burner and heater adopt different combustion and heating working fluid through free space in the past, but By using a few simple components and cleverly arranging the air flow direction, making full use of the good heat storage capacity, intense disturbance, strong heat conduction and radiation capacity of porous media; realizing the safety of preheating fresh cold air, preheating air and gas Fully mixed, fully clean combustion of the mixed gas, and the improvement of the heat exchange capacity of the heat exchanger, fully optimize the performance of the Stirling machine burner and heater.

The combustion heating system described in the patent of the present invention has the advantages of stable combustion, high combustion efficiency, good heat transfer performance, good heat storage performance, stable work, wide load adjustment range, easy adjustment, and less pollution discharge, etc., and has obvious practical value and application value.

Claims (9)

1. a combustion heating system of Stirling engine, it is characterized in that, this heating system is made of straight shape gradient stack type porous medium burner and filled type porous medium heater arranged up and down, The straight gradient stacked porous media burner includes a casing, and a gas inlet, a premixing chamber, an axial heat insulation layer, an igniter lead wire protection tube, an igniter, Gradient ceramic porous medium layer, catalytic layer, The filled porous medium heater consists of an annular insulation layer, a free space with a certain thickness, and a metal mesh cylinder from the outside to the inside. The center of the metal mesh cylinder is an air cyclone, and the center of the air cyclone is symmetrical 46 heating tubes are arranged, and the gaps of the heating tubes are filled with metal wires. 2 . The combustion heating system of a Stirling engine according to claim 1 , wherein the premixing chamber is filled with a filamentous porous medium material. 3 . 3. The combustion heating system of a Stirling engine according to claim 1, wherein the housing is a double-layer structure composed of an inner shell and an outer shell, and the inner shell is made of high temperature resistant corundum material, the outer shell includes an inner layer of thermal insulation material and an outer layer of structural steel material, and an air preheating interlayer is left between the inner shell and the outer shell. 4 . The combustion heating system of a Stirling engine according to claim 3 , wherein an air inlet is provided under the housing, and fresh air is blown from the air inlet into the air preheating interlayer by an external blower. 5 . The combustion heating system of a Stirling engine according to claim 1 , wherein the center of the axial heat insulation layer is a mixed gas injection hole, and preheating air passages are arranged around it. 5 . 6. The combustion heating system of a Stirling engine according to claim 1, wherein the igniter is a conical electric heating type igniter, and there is a certain free space near the igniter, which is made into a miniature The blunt body stabilizer is placed upstream of the main combustion area. 7. The combustion heating system of a Stirling engine according to claim 1, characterized in that, the material of the airflow swirler is high-temperature-resistant ceramics or high-temperature-resistant metal materials, and the structure is an eight-impeller structure, each The root of the blade is a straight thin slice, and the top of the blade is a quarter-arc thin slice. 8. The combustion heating system of a Stirling engine according to claim 1, characterized in that, the central position of the metal mesh cylinder is fixedly provided with an airflow swirler, and 46 swirlers are symmetrically arranged around the center of the swirler. Inverted U-shaped heating tube. 9. The combustion heating system of a Stirling engine according to claim 1, characterized in that there is a space between the metal mesh cylinder and the outer insulation layer.