SU1013726A1 - Method of utilizing heat of furnace exhaust gases - Google Patents

Abstract

METHOD OF UTILIZATION OF HEAT WASTE. Furnace gases, mainly heating gases, which include the supply of fuel and part of the exhaust gases for catalytic conversion and the supply of the converted mixture for combustion, characterized in that, in order to intensify the conversion and increase the efficiency of the process, the fuel is mixed with 20-50% of the total volume of the exhaust gases, the resulting mixture before feeding to the catalytic conversion is heated to a temperature above the temperature of the beginning of the conversion. 2. The method of claim 1, wherein the mixture and its feed to the catalytic conversion are repeated many times. §

Description

The invention relates to the technology of heat utilization of waste gases, mainly heating furnaces.

Nowadays, the share of industrial furnaces in the heat balance of the country accounts for up to 22% of the total consumed fossil fuel.

The heat released during the combustion of fuel in furnaces is only partially spent on the technological process, a large part of it from 50% to 70% is lost with the leaving combustion products.

In this connection, a great deal of attention has recently been paid to solving the problem of utilizing heat from waste gases.

New, efficient ways of utilizing heat from flue gases are being developed, based on thermochemical heat recovery, which transfers heat as chemical energy to the fuel. The essence of such a regeneration is that the organic fuel is heat treated with a coolant which undergoes an endothermic reaction with the fuel, for example, by the reaction between methane, carbon dioxide 1M gas and water vapor CH + H. , 3 kcal / mol (1), СН4 + СО..2СО + 2Н ..- 59.1 kcal / mol (2)

As heat carriers, they are used to mix organic fuel with air and water vapor.

A known method of utilizing heat from waste gases is based on thermochemical heat recovery involving mixing the fuel — methane with coolant, heating the mixture, carrying out the catalytic conversion of the mixture obtained and returning the converted gas to the furnace. burning. Steam is used as a heat carrier, which is mixed with fuel in a stoichiometric ratio. The method is carried out in a reactor to which water vapor, fuel and a catalyst for the conversion of methane, for example ... brand ICH, are simultaneously fed. In the resulting mixture, the endothermic reaction of steam reforming of methane occurs, in the result of which thermal energy is stored, which is reused in industrial furnaces Cl.

However, this method is not effective enough due to the low intensity of steam reforming of methane. In addition, steam conversion has another drawback; it requires a large amount of water vapor (1.125 kg and 1 kg of methane), and about 6% of the heat from incineration is spent on its heating. natural gas. Besides.

the implementation of heating the entire mixture with the catalyst leads to a rapid destruction of the catalyst.

The closest to the present invention is a method based on thermochemical heat recovery, using part of the exhaust gases as heat carrier.

This process is more economical, since the waste gases are used not for heating the heat carrier, but directly as the heat carrier 2 D-.

However, in the known method, the conversion of fuel with part of the flue gases is carried out in a chemical reactor that combines the functions of three units — a mixer, a mixture heater, and. reactor. Such a formalization of the conversion process is possible if the heat content of flue gases is sufficient for carrying out endothermic reactions of their reduction (for example, exhaust gases from a MHD generator T of 22002500 K).

At lower temperatures, flue gases (T 1200 K) or for fuel, the direct supply of which to the combustion products is accompanied by carbon black (for example, when methane is supplied to its combustion products), such a design of the conversion process is impossible.

In this case, it is necessary to use a catalyst, which significantly reduces the temperature of the start of the recovery of exhaust gases with organic fuel, as well as additional heating of the mixture from the outside. However, optimal conversion and heating in one unit is not possible, because to intensify heat transfer, an increase in the rate of movement of the mixture along the footing surface is necessary, and to intensify the conversion process, a decrease in speed, i.e. an increase in the residence time of the mixture in the catalyst. In addition, the presence of a catalyst, the thermal conductivity of which is small, does not contribute to an increase in the heat supply either at high or at low flow rates of the mixture. R

The purpose of the invention is to intensify

conversion and increase the efficiency of the process.

The goal is achieved by the fact that according to the method of heat recovery of waste gases from furnaces, mainly heating, including the supply of fuel and part of the exhaust gases to the catalytic conversion and the supply of the converted mixture of gases to combustion, the fuel is mixed with 20-50% of the total amount of exhaust gases, received

laugh pirel filing for catalytic. Whichever sonversion is heated to a temperature above the temperature of the beginning of the conversion.

In addition, heating the mixture and feeding it to the catalytic conversion are repeated many times.

The drawing shows the scheme, the implementation of the method. .

The circuit contains a commercial furnace 1, an air preheater 2, a mixture preheater 3, a chemical reactor for conversion 4, and a mixer 5.

Utilization of the heat of the heating furnace according to the proposed method is carried out as follows.

Organic: some fuel and 20-50% of exhaust gases (depending on the type of furnace and the selected technological scheme) are passed into the mixer. 5, where the mixture formation takes place and it is fed to the mixing heater 3. After heating to a temperature above the start temperature of the catalytic conversion (for methane this temperature is 1100 K and exceeds the start temperature of the methane conversion on the nickel catalyst by 50 -) , the mixture is directed to chemical reactor 4 where the organic top is converted; with its own combustion products — waste gases, according to reactions (1) and (2). Heat is required for exothermic reactions (1) and (2). . A portion of the physical heat of the combustion products exiting the furnace is spent on the implementation of these reactions and is converted into chemical energy from the products of thermal conversion and with them returns to the furnace.

The proposed method was tested on the KORT-M experimental setup: simulating the operation of a continuous furnace,. running on natural gas ...

The basic scheme of the experimental setup for the implementation of the proposed method corresponds to the drawing. It consists of its own furnace, a pissection air preheater, a four-section preheater of the converted gas (a mixture preheater), three adiabatic chemical reactors filled with a KSN catalyst, an injection mixer and a water calorimeter (not shown). The furnace is made in the form of a rectangular channel 250x250, 1500 mm high and is lined with a high-alumina ultralight weight 125 mm. The furnace volume is divided by a ceramic nozzle into a combustion chamber and a heat removal section. In the latter, a water calorimeter of the coil type is installed to change the temperature of the gases. The air heater and mixing heater are made in a bidet of one technological device consisting of ten sections of tubular heaters, each of which consists of seven heat-resistant pipes. An air heater is located in five sections, four heaters of the converted gases are located in the fixed section, and combustion products are selected through perforated pipes in the sectional section. .

The size of the tract heating products of combustion 250x250, the height of one.

80 mm sections.

The operation of the furnace is carried out as follows. Air and converted gas are supplied to the furnace through the path of the tubular preheaters. The furnace burns the mixture and the combustion products are directed to a water calorimeter, imitating a useful technological process. After

doing useful work, the combustion products are fed to the pipes of the preheater of the converted gas. The temperature of the combustion products at the entrance to the heaters can vary from 1500 to 400 K, which

covers almost the entire range of temperature variations of interest.

Methane is mixed into the preheater and mixed with the combustion product. The design of the plant ensures stable operation over a wide range of changes in the oxidizer excess coefficients d.0.7-2.0. After warming up to a mixture of methane with combustion products, it enters the Ni-catalyst of the KSN brand, where the formation of the converted gas occurs, which enters the furnace

on combustion. ..

To intensify the process, con-. versions that are accompanied by significant heat absorption, the converted gas preheater is performed in four sections (preheat-convert on catalyst; preheat-convert, etc.).

The results of the experiments confirmed the efficiency of the separation of the heat exchange process and catalytic conversion in the organization of various technological schemes. In this case, no soot release occurred on the catalyst.

60 The studies performed confirmed the efficiency of the circuit as a whole and its individual elements.

The use of a furnace with thermochemical heat recovery is

It is a promising direction for increasing fuel efficiency in the national economy and will make it possible to reduce specific fuel consumption in a number of productions by 15–20% compared with air-only heat recovery.

The constructive design of the chemical reactor with the separation of heat exchange processes and catalytic conversion contributes to the intensification of the process of heating the mixture by 2-3 times and increases the service life of the catalyst by 1.5-2 times.

Claims (2)

METHOD FOR DISPOSAL OF FURNACE HEATS OF FURNACE GASES OF FURNACES, predominantly heating, including the supply of fuel and part of the exhaust gases to catalytic conversion and the supply of the converted mixture of gases for combustion, characterized in that, in order to intensify the conversion and increase the efficiency of the process, the fuel is mixed with 20 50% the total amount of exhaust gas, the resulting mixture is heated to a temperature above the start of conversion before being fed to the catalytic conversion. 2. The method of pop. 1, characterized in that the mixture is heated and fed to the catalytic conversion repeatedly. »SU ..., 1013726 I 0137 26 t