RU2305129C1 - Method of utilizing fuel in superadiabatic mode - Google Patents

Abstract

FIELD: heat engineering.

SUBSTANCE: invention is directed heat supply of buildings and constructions, and for various technological needs requiring hot water, steam, and hot air. In a method of utilizing fuel under superadiabatic two-step filtration burning to form synthesis gas (for further use with excess of oxidant), process temperature is raised and maintained at a level of 2000-2300 K by way of raising fuel heating temperature Tn within 350°C < Tn < 500°C owing to additional recuperation of heat. Through that, water dissociation step is achieved resulting in releasing hydrogen involved in the fuel burning process.

EFFECT: enabled utilization of alcohol hydrocarbon fuel types, including low-grade types, in particular wastes from forestry, wood working, hydrolysis, and agricultural industries, shales, brown coal, domestic garbage, and gaseous fuel.

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Description

The invention relates to a power system and can be used for heat supply of buildings and structures, for various technological needs, using hot water, steam and hot air. The method allows to utilize all types of hydrocarbon fuel, including its low-quality types: substandard coal methane, waste from logging, woodworking, hydrolysis, agricultural and other industries, shale, brown coal, household waste.

The application of the proposed method will allow to utilize many of these materials, currently used in limited ways. Utilization of renewable types of hydrocarbons will reduce the consumption of non-renewable types of high-quality raw materials: coal, natural gas, liquid fuel, etc.

A known method of burning solid fuels in two stages / 1 /. At the first stage, air or steam conversion is carried out with a lack of an oxidizing agent to produce synthesis gas containing hydrogen H ₂ , carbon monoxide CO, and other organic compounds burned in the furnaces of heat-generating devices in the second stage.

The disadvantage of this method is the lack of both temporary and operational parameters of the optimization of the conversion mode.

There is also known a method / 2 /, the closest in technical essence and the achieved result to the claimed one, which is a process of filtration combustion in a super-adiabatic mode with temperatures exceeding the temperature of adiabatic combustion.

The technical result of the invention is the implementation of the process of utilizing substandard types of fuel (peat, brown coal, firewood, oil shale, household waste, oil and gas production waste, etc.).

The technical result is achieved by providing the possibility of fuel utilization by creating high temperatures in the regime of super-adiabatic combustion.

In the method of fuel utilization in the super-adiabatic mode by means of two-stage filtration combustion with heat recovery, synthesis gas formation and its subsequent utilization with an excess of oxidizing agent, the process temperature in the second stage is increased and maintained at the level of 2000-2300K by increasing the fuel heating temperature within 350 <T < 500 ° C due to additional heat recovery, while reaching the stage of dissociation of water to produce hydrogen, which is involved in the combustion process, as fuel.

The proposed method is illustrated by the installation diagram for implementing the method and graphs.

Figure 1 shows a gas generator with external and internal heat recovery and a process diagram: the gas generator contains a device 1 for loading fuel, a reactor 2 with a chamber 3 for the formation of synthesis gas, a recuperator 4, an ash pan 5, a channel 6 for primary air, a grate 7 , a flame tube 8, a primary combustion chamber 9, a secondary air channel 10, a furnace 11 of a power plant.

Figure 2 is a graph of the calculated dependence of the exit to the stationary mode of the conversion plant on the mass of the loaded substance - In _m , kg

Figure 3 is a graph showing the nature of the influence of moisture on the combustion process of the second stage, determined by the temperature level in the furnace 11 of the power plant and the temperature of the fuel heating.

The method is implemented as follows.

Solid wet fuel is loaded into the device 1 of the gas generator, a certain amount of primary air is fed into the reactor 2 through the channel 6, the mixture is ignited and heating of the loaded fuel begins, accompanied by the formation of synthesis gas. The synthesis gas enters the flame tube 8, where secondary air is supplied through the channel 10 in an amount ensuring complete combustion of the synthesis gas. The combustion products in accordance with technological requirements are distributed between the recuperator 4 and the furnace 11 of the power plant.

The graph (figure 2) of the calculated dependence of the exit to the stationary mode allows you to calculate the time to exit to the stationary mode of the conversion plant depending on the mass of the loaded substance - B _m (kg) and the temperature in the recuperator.

The invention consists in the utilization of solid wet fuels (peat, brown coal, firewood, oil shale, household waste, oil and gas waste, etc.) at high temperatures in the regime of super-adiabatic combustion to produce synthesis gas and use it as a gaseous fuel in energy installations.

The method can also be used for the disposal of substandard mixtures of coal methane with air. At present, a substandard explosive mixture of coal methane with air (methane content varies between 2.5-25% vol.) Is removed to the atmosphere. The proposed method may allow to utilize substandard mixtures of coal methane, including when co-burning it with solid fuels. A gas-air mixture with a coal methane content of less than 2.5% by volume can be used in this installation as a blast for burning solid fuel. Installation for implementing the method of fuel utilization can be mounted in the immediate vicinity of the place of extraction of coal methane.

The super-adiabatic combustion mode is achieved due to:

- combustion in a hydrogen reactor H ₂ formed during the thermal decomposition of hydrocarbon fuels and during the dissociation of water at temperatures above 2000K, and having a high calorific value; a diffusion flow of hydrogen having a high diffusion coefficient D exceeding the coefficient of thermal diffusivity and thermal decomposition of fuel; additional supply of thermal energy to the high-temperature zone of thermal air or steam-air conversion of the starting fuel and providing heat transfer from the recuperator 4 located in the outer part of the reactor 2, into which the utilized fuel is loaded.

When burning wet hydrocarbon fuel in a traditional way, moisture reduces its heat and combustion temperature due to the endothermy of evaporation and heating of water. At fuel heating temperatures Tn <350 ° C, the combustion temperature and thermal effects decrease with increasing relative humidity of the fuel, and at Tn> 350 ° C they increase. The combustion temperatures developing in this case at T <350 ° C are lower than the adiabatic combustion temperatures for the corresponding type of fuel, and at T> 350 ° C they are higher, i.e. one of the adiabatic combustion regimes begins to be realized. Thus, the optimum temperature range for fuel heating is 350 <T <500 ° C.

Fuel is loaded into a gas generator with a recuperator, where in the initial period of time the fuel is heated to a conversion temperature. Further, the conversion process is carried out in a stationary mode.

The time for reaching the stationary mode of the gas generator is determined by the mass of the loaded substance, the temperature level in the reaction zone.

The process of fuel utilization is carried out in two stages.

The first stage (steam, air or steam-air fuel conversion) occurs with a lack of oxidizing agent (the nature of the conversion depends on the type of oxidizing agent - hot water vapor, air, air mixture with steam) with the formation of synthesis gas.

In the second stage, the synthesis gas is disposed of in heat / power generating devices (boilers, turbines, internal combustion engines) with an excess of oxidizing agent, which ensures complete combustion of the synthesis gas.

The achievement of the super-adiabatic regime is carried out due to external and internal heat recovery. Internal recovery is due, in particular, to the amount of hydrogen generated as a result of the thermal decomposition of hydrocarbon fuels and the dissociation of water originally contained in the fuel. External recovery is provided by supplying to the heat-insulated heat exchanger the required amount of heat, determined by:

- the release of volatile combustible components from the substance loaded into the reactor - β;

- the proportion of combustion products supplied to the recuperator - β ₁ ;

- the flow rate of the substance loaded into the reactor is B _m ;

;- the heat of combustion of the resulting synthesis gas -

;

- the time the unit goes to stationary mode - t,

depending on the mass of the loaded substance, the temperature level in the recuperator, determined by the convective and radiation components of the heat transfer from the recuperator to the reactor, heat loss to the surrounding space.

Example 1

The super-adiabatic combustion mode is achieved due to the combustion of hydrogen Н ₂ in the reactor, which is formed during the thermal decomposition of hydrocarbon fuel and the dissociation of water at temperatures of 2000-2300K, which has a high heat of combustion. The filtration process of combustion consists in the penetration of a diffusion stream of hydrogen towards the incoming mass of fuel. Hydrogen has a high diffusion coefficient D, which exceeds the thermal diffusivity. An additional supply of thermal energy to the high-temperature zone of thermal air or steam-air conversion of the initial fuel and heat transfer from the recuperator 4 located in the outer part of the reactor 2, into which the utilized fuel is loaded, provide a two-stage process of thermal decomposition and further combustion of the fuel.

First stage

Solid fuel - peat of the following composition is loaded into gas generator device 1: C _48.12 H _59.52 S _0.094 O _20.875 N _1.785 , where the indices indicate the element composition in gram atoms (C - carbon, H - hydrogen, S - sulfur, O - oxygen, N - nitrogen) per 1 kg of fuel. The mass of the loaded fuel is determined by its density, the volume of the receiving device 1 and is equal to M _t = 50 kg.

The fuel is heated at temperatures 350 <T <500 ° C, in particular at T 435 ° C, the combustion temperature and specific heat increase significantly with increasing fuel moisture.

Air blast is fed to the reactor 2 through channel 6, the flow rate of which depends on the mass of the loaded fuel, the arson mode and the gasification process, characterized by the value of the oxygen-containing blast flow coefficient (α).

The ignition of the fuel is carried out in the chamber 3 for the formation of synthesis gas, which is 10% of the volume of the device 1 for loading fuel, with a stoichiometric ratio of oxidizer and fuel equal to A = 7.26 kg of air / kg of peat. In this example, the air flow rate is 20 kg / h.

The heating of the fuel begins, the time of which is determined by the values of the parameters:

- the exit of volatile combustible components from the fuel loaded into the reactor, equal to peat β = 0.47 ÷ 0.53;

- flow rate of fuel loaded into the reactor B _m = 50 kg / h;

;- the heat of combustion of the resulting synthesis gas

;

- the mass of fuel loaded into the hopper M _t = 50 kg;

- the temperature level in the reaction zone T _g = 930-1200K;

и радиационной

составляющими теплопередачи от стенки рекуператора к пиролизуемой массе топлива;- convective coefficients

and radiation

heat transfer components from the wall of the recuperator to the pyrolyzable mass of fuel;

- the degree of blackness of the inner surface of the recuperator ∈ _m = 0.8;

- heat loss to the surrounding space η _sweat = 0.6-0.85.

When loading 50 kg of fuel into the hopper, the heating time is 0.6 hours, when loading 100 kg - 1.2 hours, 200 kg - 2.4 hours, 400 kg - 5 hours.

Upon reaching the stationary mode, the gas generation process in chamber 3 for the formation of synthesis gas is carried out at an air oxidizer consumption coefficient α = 0.3, with a characteristic maximum synthesis gas yield of 47% (CO + H ₂ ) depending on α. The indicated value of α corresponds to the temperature Tk = 930K, to which the fuel is heated in reactor 2. The consumption of air blast for pyrolysis of peat is 5 kg / h.

An increase in the relative humidity of previously unheated peat from 0 to 50% reduces the temperature of gas generation by 200 degrees, which is accompanied by a decrease in the yield of synthesis gas by 4% (from 47 to 43%).

An increase in the proportion of synthesis gas from the pyrolyzable mass of peat in the reactor 2 to 53% was obtained experimentally with an increase in the pyrolysis temperature of the fuel to T = 1200K, achieved by feeding 30% of the combustion products from the furnace 11 to the recuperator.

Second stage

The synthesis gas is fed into the flame tube 8, secondary air is supplied through the channel 10 with a flow rate of 14.5 kg / h, which ensures complete combustion of the synthesis gas. The combustion begins in the primary combustion chamber 9 and ends in the furnace 11 of the power plant. The total coefficient of consumption of the air oxidizer is α = 1.15, taking into account primary air.

Experimentally confirmed (figure 3) that the nature of the influence of moisture on the combustion process of the second stage is determined by the temperature level in the furnace 11 of the power plant, depending on the temperature of the fuel heating. During the initial heating of the fuel, carried out, in particular, with the help of a recuperator 4 from 20 to 350 ° C, the combustion temperature decreases with an increase in humidity from 2218 to 2010K. A further increase in the temperature of fuel heating (> 350 ° C), in particular up to 435 ° C, is characterized by an increase in the temperature of synthesis gas combustion from 2218 to 2270K and specific heat with an increase in the humidity of the fuel. Additional heat recovery is provided by reaching the stage of water dissociation to produce hydrogen, which is involved in the combustion process as fuel. An increase in the temperature of heating the entire mass of fuel in the device 1 is provided by an increase in heat stress in the recuperator 4, which is achieved by increasing the amount of combustion products supplied to the recuperator 4 to 30%. The heat intensity in the recuperator 4 also increases with increasing combustion temperature in the furnace 11.

Example 2 of the method for the supply of gaseous fuel

The super-adiabatic combustion mode is achieved due to the combustion of hydrogen Н ₂ in the reactor, which is formed during the thermal decomposition of hydrocarbon fuel and the dissociation of water at temperatures of 2000-2300K, which has a high heat of combustion. The filtration process of combustion consists in the penetration of a diffusion stream of hydrogen towards the incoming mass of fuel. Hydrogen has a high diffusion coefficient D, which exceeds the thermal diffusivity. An additional supply of thermal energy to the high-temperature zone of thermal air or steam-air conversion of the initial fuel and heat transfer from the recuperator 4 located in the outer part of the reactor 2, into which the utilized fuel is loaded, provide a two-stage process of thermal decomposition and further combustion of the fuel.

When utilizing gaseous fuels (with small additions of solid hydrocarbon feedstocks), the gas generator is waterproofed from the surrounding area.

First stage

Mine methane (a methane-air mixture of variable composition and flow rate removed from coal mines by vacuum pumps) of substandard composition with a methane content of 16 to 25% (vol.) Is fed to gas generator device 1. Substandard is a methane-air mixture with a methane content of 2.5 to 25% (vol.). Mixtures with a methane content of 5 to 15% are explosive and are released into the atmosphere. Methane-air mixtures with a methane content of 2.5 to 5% can be disposed of in gas generators as blast.

In this example, 22% methane-air mixture (with solid additives up to 1%) is fed to the gas generator - fuel. The mass of the loaded fuel is determined by the volume of the receiving device 1, the density of the fuel and is equal to M _t = 100 kg. Ignition of the fuel is carried out by feeding air blast into the reactor 2 through channel 6, the flow rate of which is determined by the mass and composition of the loaded fuel. Heating fuel from 20 to 350 ° C reduces the combustion temperature as humidity increases. An increase in the temperature of fuel heating (> 350 ° C), in particular up to 500 ° C, contributes to an increase in the combustion temperature. Ignition of the fuel is carried out in the chamber for the formation of synthesis gas 3, which is 20% of the volume of the device for loading fuel 1. With a stoichiometric ratio of oxidizer and fuel equal to A = 17.2 kg of air / kg of fuel, 210 kg of air is supplied to chamber 3. After ignition of the mixture, the supply of primary blast is stopped. The heating of the loaded fuel begins, which is accompanied by conversion (chemical conversion) with the formation of synthesis gas. The heating time of the loaded mixture is determined by the mass of fuel in the gas generator M _t = 100 kg, fuel consumption B _m = 50 kg / h, the heat of combustion of the resulting synthesis gas, the temperature level in chamber 3, the coefficients of the convective and radiation components of the heat transfer from the heat exchanger wall to the converted mass , the degree of blackness of the inner surface of the recuperator, heat loss to the surrounding space.

When entering the stationary mode, the conversion process in the synthesis gas production chamber 3 is carried out with an air oxidizer consumption coefficient α = 0.37. Air conversion is accompanied by the formation of synthesis gas (H ₂ , H ₂ O, N ₂ , NH ₃ , CO, CO ₂ , CH ₄ ), the calorific value of which depends on the amount of (CO + H ₂ ) in its composition.

The increase in the proportion of synthesis gas from 35.8 to 43.5% with an increase in the conversion temperature from 900 to 1200K, achieved by supplying 4 products of combustion from the furnace of the power plant 11 to the recuperator, was experimentally confirmed.

Second stage

The synthesis gas is fed into the flame tube 8, secondary air is supplied through the channel 10 with a flow rate of 14.5 kg / h, which ensures complete combustion of the synthesis gas. The combustion begins in the primary combustion chamber 9 and ends in the furnace 11 of the power plant. The total coefficient of consumption of the air oxidizer, taking into account the primary air, is α = 1.15. The adiabatic combustion temperature of the synthesis gas in the air blast is 2090K, the achievement of which in real conditions requires increased thermal insulation of the furnace 11 of the power plant. The course of the combustion process in the second stage is determined by the initial heat content of the fuel, depending on its pre-heating, and relative humidity. Additional heat recovery is provided by reaching the stage of water dissociation to produce hydrogen, which is involved in the combustion process as fuel.

The nature of the influence of moisture on the combustion process is determined by the temperature level in the furnace 11 of the power plant, depending on the temperature of the fuel heating. When fuel is heated using recuperator 4 from 20 to 350 ° C, the combustion temperature decreases with increasing humidity from 2090 to 1920K. A further increase in the temperature of fuel heating (> 350 ° C), in particular up to 500 ° C, is characterized by an increase in the temperature of combustion of synthesis gas from 2090 to 2300K and specific heat with an increase in the humidity of the fuel. When the process reaches the indicated temperatures, it provides the stage of water dissociation to produce hydrogen involved in the combustion process as fuel.

The implementation of the method of fuel utilization in high temperature mode allows to obtain synthesis gas, which can be used as gaseous fuel in power plants to produce thermal or (and) electric energy, as well as in process plants for producing hydrogen, synthetic motor fuel.

List of sources used

1. Bokhan N.I., Lovkis V.B., Nosko V.V., Falyushin N.I. Gas generators. - News of heat supply, 2004, No. 8, p.16-18.

2. Manelis G.B., Fursov V.P., Stesik L.N., Yakovleva G.S., Polianchik E.V., Alkov N.G. A method of processing waste containing hydrocarbons. RF patent No. RU 02116570 C1 19980727.

Claims (1)

The method of fuel utilization in super-adiabatic mode by means of two-stage filtration combustion with the formation of synthesis gas, followed by its utilization with an excess of oxidizing agent, characterized in that the process temperature is maintained at 2000-2300 K by increasing the fuel heating temperature Tn within 350 ° C <Tn <500 ° C due to additional heat recovery with reaching the stage of water dissociation with the production of hydrogen involved in the combustion process as fuel.

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