FR2465777A1 - Conversion of coal by drying, pyrolysis and gasification - using recycled coke as heat carrier - Google Patents

Abstract

Conversion of particulate coal (or other solid fuel) to liq. and gaseous products is carried out by (a) drying the coal in contact with a heat carrier comprising recycled particulate coke; (b) subjecting the coal/coke mixt. ot pyrolysis in 2 stages and recycling part of the coke to step (a); (c) heating the rest of the coke to 800-1500 deg.C. by contact with hot gaes and/or by partial combustion; and (d) steam-gasifying the hot coke and recycling residual coke to the 1st pyrolysis stage. The process is stated to have a thermal efficiency of 84-88% and to give high yields of high-quality products (pyrolysis gas, liq. hydrocarbons and water gas).

Description

 The present invention relates to the field of multiple energy and technological transformation of fuels, and more specifically relates to a thermal transformation process of a ground solid fuel.

 The proposed invention will find wide application in the production of transportable fuels including artificial combustible liquids, electrical energy, as well as technical and chemical raw materials.

There is a known process for the thermal transformation of a solid fuel in which, as heat transfer agent for heating said fuel, corundum balls are used whose diameter is between 10 and 12 mm and which are heated in a first chamber of a reactor. to two chambers by the combustion gases. In the second chamber, into which a hot balance heat transfer agent is continuously fed from above, heating, final drying, coking and partial gasification of the ground solid fuel which rises mixed with the gas and steam takes place. through a compact layer of heat transfer agent from bottom to top. As marketable products hot coke, a resin and a gas are obtained. (Perepelitsa A.L. et al. "Use of a solid heat transfer agent in the continuous coking cycle of coals in the Irkutsk basin").

 There is known a process for the thermal transformation of a solid fuel according to which a stream of a gaseous suspension of the solid fuel is heated from the bottom upwards, heated by a downward flow directed against it containing the larger heated particles of solid heat transfer agent (sand, fractionated particles, etc.) which do not mix with the fuel. Together with the solid fuel, steam is introduced into the reactor and at the same time as the pyrolysis, the process of gasification of coal takes place. In this case, the heat transfer agent is heated by the stack gases which do not mix with the products resulting from the pyrolysis and gasification. (see USSR author's certificate NO 82492).

The aforementioned process is characterized by a dilution of the products resulting from the pyrolysis by steam.
water and gas to water, making the epu more complicated
ration and use of products resulting from pyrolysis as well as the construction of apparatus.

A process for the pyrolysis of a fuel is known
solid consisting of coal, comprising drying
coal, heating the coal to the
temperature of 5000C being assured in a first zone
pyrolysis by the heat given off by the stack gases
obtaining small coke, introducing small coke
in the second pyrolysis zone and its heating to the temperature of 100,000 by a gaseous heat transfer agent
with release of residual pyrolysis products
and small coke, and their subsequent separation and eva-
cuation in the form of commercial products (certificate
from the USSR NO 335267).

The above method is characterized in that
the solid fuel residue, the small coke, obtained at
following pyrolysis and gasification together
with ashes is commonly used in homes
of the boiler of a technical energy installation,
which makes the operation of the installation complicated
energy (from the boiler) due to the formation of
dairy and environmental pollution by dice
harmful waste such as oxides of sulfur and nitrogen,
as well as by ash particles; the yield in
valuable organic products is reduced there and these products
are diluted by harmful impurities.

The object of the invention is to implement a
thermal transformation process of a ground solid fuel by modification of technological operations, which
would have a higher yield and at the same time a
increase in yield of products to be obtained and a
improving the quality of these products and which allows
trait to avoid the formation of slag in boilers
power generation facilities and the
pollution of the surrounding environment by harmful impurities.

 The aim is achieved by implementing a process for the thermal transformation of a ground solid fuel comprising the stage of drying said fuel and its pyrolysis in two stages, followed by a subsequent separation of the gaseous products and the vapors which form. and small coke, characterized in that the drying of said fuel is partially carried out by a part of said small heated coke, at least a part of the small coke which remains being further heated to a temperature between 800 and 15000C by the gases and / or by a partial combustion of the small coke, after which the heated small coke is separated from the gases and subjected to gasification using steam obtained during the drying of said fuel, the products formed resulting from the gasification then being separated from the small coke which is then brought as heat transfer agent in the first stage of pyrolysis.

The proposed process is very efficient, it has a high energy efficiency (from 84 to 88in) s which becomes possible thanks to the use of small coke and water vapor obtained from the humidity contained in the fuel for the gasification process in the event of complex chemical, technological and energy use of raw materials.

 In addition, the process of the invention makes it possible to use the thermal potential of the heat transfer agent in a rational manner, thereby increasing the efficiency of the process. The use for pyrolysis of a solid heat transfer agent such as small ccke, cooled during the gasification gives the possibility of carrying out the pyrolysis at a milder thermal regime, that is to say with a decrease in the difference in temperatures of the heat transfer agent at the first stage of pyrolysis, which makes it possible to: increase the yield of the most precious liquid products resulting from very rapid pyrolysis.

Since the small coke reaches an excess gasification, the quantity of which is conditioned by the thermal balance of the gas to water reactor, the water vapor has a high degree and an intensity of decomposition, as well as a yield high production of gas to water.

 It is advantageous to intensify and regulate the processes of heating the fuel and its drying, to carry out said operations in a stream of superheated steam and to bring to the first stage of the pyrolysis part of the gases separated from the small heated coke.

 It is advantageous, to make the process more intense and to increase the yield of expensive gaseous products resulting from the pyrolysis, to use a crushed solid fuel whose particle size does not exceed 1.5 mm and that the gases supplied to the first Pyrolysis stage contain only 2% by volume of free oxygen.

The proposed process is carried out as follows and is explained by the appended drawing in which the preferred technological scheme for carrying out the process is shown.

According to the accompanying drawing, a ground solid fuel whose particle size is preferably not more than 1.5 mm is brought from a hopper 1 to a hammer mill 2 into which, for its grinding and drying, is introduced through a tube 3 by conduits 4, 5 part of the small coke obtained during the pyrolysis, and by means of a fan 6, water vapor. A gaseous suspension is introduced through a pipe 7, into a cyclone 8 in which the separation of said dry fuel is carried out, while the superheated water vapor formed by the humidity contained in the fuel is brought through the fan 6 by a pipe. 9, through a grid 11 in a water gas reactor and partially in the grinder 2. However, it is possible to carry out the abovementioned processes of drying and heating the fuel without supplying superheated steam.

The aforementioned dry fuel is introduced through an intermediate closing hopper 12, into a pyrolyser of the first stage 13 into which, through a line 14, a solid heat transfer agent, small coke, or a mixed heat transfer agent (solid or gaseous) is also introduced. ) which heats the aforementioned fuel to a temperature of between 500 and 8000 C. The products resulting from the pyrolysis together with an insignificant part of the small powdery coke are sent into a cyclone 15 in which the small coke sent is separated into intermediate hoppers 16 , 17 and is then used as a heat transfer agent for pyrolysis, or as a transportable combustible product which is put on the market.

The gas-vapor mixture of cyclone 15 is sent through a line 18 to a purification and condensation system in which liquid products of commercial value and gas are obtained.

 Part of the small hot coke from the pyrolyzer 13 is introduced via line 4, through the pipe 3 into the grinder 2, the small coke which remains arrives in the second stage pyrolyzer 19 in which it is heated to a temperature comprised between 600 and 11000C using a gas burner 20 supplied with a gas supplied together with the air by inlets 21. The gas coming from the second stage pyrolyzer 19 and from the hopper 17 is evacuated through nozzles by gas lines 22.

 Part of the small coke from the second stage pyrolyser 19 is brought from the crusher 2 through the pipe 5 through the pipe 3, the small coke which remains arrives from the second stage pyrolyser 19 in a technological center 23 connected to a cyclone 24. It is possible to introduce only part of the small hot coke coming from the pyrolyser of the second stage 19 in the technological center 23; in this case, the part of the small coke which remains in the form of a commercial product is eliminated from the process by a line 33. In the technological center 23, a gas burner 25 is used using the gas supplied together with l air through inlets 26, the main (second) part of the gaseous heat transfer agent which heats and transports the small coke, the solid heat transfer agent being brought through the technological center 23 in the cyclone 24.

 The small coke which is released at a temperature between 800 and 15000C in the cyclone 24 is brought through an intermediate hopper 27 into the water gas reactor 11 in which a portion of the required small coke is gasified by introduction by the pipe 9 through the grid 10 of the water vapor obtained from the humidity contained in the fuel, and in the event of its insufficiency, by introduction of the steam arriving through a pipe 28. The water vapor in the water to gas reactor 11 turns into a high calorie water gas 11 which is a valuable starting chemical and fuel. The gaseous suspension of gas to water and small coke is sent from the gas to water reactor 11 in a cyclone 29 in which the small coke is separated from the gas to water and it is introduced as a solid heat transfer agent through a hopper 30 into line 14 in which is mixed with a part of gas leaving the cyc lone 24. The essential part of the gas is evacuated through a pipe 31 for purification and brought into an energy group. It is also possible to carry out the process without introducing the gas into the pyrolyzer 13. In the case of the above-mentioned mixture of the solid heat-transfer agent with part of the gas, the mixed heat-transfer agent obtained is brought to the pyrolyser of the first stage 13.

 Thus, in the proposed process, thanks to the implementation of the closed cycle of pyrolysis, gasification and drying, harmful emissions into the atmosphere are excluded, since the mixed gases, with water and pyrolysis arriving in the homes of the energy units are purified. This is why it becomes possible to significantly reduce the dimensions (height) of the boilers of the energy units and to make their operation simpler.

 Besides this, since in the proposed process water vapor obtained during the drying of the fuel for its production is used for gasification, there is no need to consume an additional fuel. This significantly increases the energy efficiency of the fuel used by 3 to 5%.

 The water gas (mainly hydrogen and carbon oxides) of the cyclone 29 is sent for purification through a pipe 32 and then it is supplied to a user who can be an industrial energy production installation. , including a gas turbine or chemical reactor for the production of hydrogen, synthesis gas, methanol and other products.

The proposed process makes it possible to produce a very inexpensive water gas, since the excess of small coke in the water gas reactor II ensures a high degree (from 80 to 95%) of decomposition of water vapor and obtaining a high energy yield as well as making the system as a whole simpler. Automatic regulation of the production of a necessary quantity of gas to the water, of the process temperature and of the quantity of the solid heat transfer agent in circulation constituted by small coke, is carried out by modification of the evacuation of the small coke out of the process through the intermediate hopper 17 by a line 33 and the supply of steam in the gas to water reactor 11 taking into consideration a possible change in the quality of the fuel and the operating regime of the energy unit. The valves used for regulating the corresponding streams of steam, gas, gaseous suspension and solid particles are not shown in the drawing.

 A very important feature characterizing the process of the invention lies in the fact that into the furnace of the boiler of an energy unit are introduced gases which are completely rid of sulfur, solid fuel and ash, thereby excluding the formation of slag on the heating surfaces. This process is very economical when using peat, especially peat with very high humidity. The size of the boilers is very small.

 The temperature regime of the pyrolysis and gasification is adjusted by varying the quantity and the temperature of the gaseous heat transfer agent obtained in the gas burners 20, 25 and in the technological center 23.

 Since a large quantity of a low-calorie gas, a semi-gas, obtained in the technological center 23 is introduced into the furnace of the boiler of an industrial energy production installation. and in the burners 20, 25, the combustion temperature prevailing in the hearth of an energy unit decreases and the content of harmful nitrogen oxides in the gases of the energy units decreases suddenly thanks to the nitrogen oxides, both external (forming in the hearth during the burning of nitrogen) than inside (released from the nitrogen contained in the fuel) obtained during the transformation of said fuels in an industrial energy production installation. This not only makes it possible to use in a complete manner said fuel in such an installation, but almost completely avoiding pollution of the surrounding environment by discharges containing gaseous (oxides of sulfur and nitrogen) and solid (particulate es of the ashes) arriving in the atmosphere from the installation.

The proposed method also makes it possible to use low-quality energetic liquid fuels by introducing them into a technological furnace or into a water gas reactor depending on the destination of the water gas to be produced.

Below are examples of the embodiment of the process of the invention.

Example 1
We examine the operation of an industrial power plant with thermal transformation of coal. The power of a unit installation is 500 tonnes of raw coal per hour. The power of the installation is 50 million tonnes of coal per year, and as regards the electrical energy produced, this power is 32 billion kilowatts / hour per year.

The thermal transformation of the raw coal is carried out, the calorific value of which is 3560 kcal / kg and which contains 36% by weight of moisture, 6.5% by weight of ash and 48% by weight of volatile substances relative to the mass. combustible. The coal from the hopper 1 is introduced into the dryer mill 2 in which for every 100 kg of coal a circulating mixture is introduced through the tube 3 containing 120 kg of small coke (soliae coolant) and 80 kg of steam , heated respectively to temperatures of 7800C and 5800C. The products to be dried, 64 kg of dry powdery charcoal (the residue on a 100 micron sieve is 10% by weight) and 36 kg of steam at a temperature of 2500C are passed together with the heat transfer agent through cyclone 8 in which the coal and small coke are separated from the water value.

 The steam taken in an amount of 36 kg is introduced into the gas-to-water reactor 11 and 80 kg of steam is brought in for circulation in the grinder 2.

In case of excess steam obtained from the coals, which in this example amounts to 18 kg, it is also possible to send it to the hearth of the energy unit. The dry coal in an amount of 64 kg, the small coke at the rate of 120 kg at the temperature of 2500C are brought through the intermediate hopper 12 in the pyrolyser of the first stage 13 and the temperature is brought up to 6800C using l '' mixed heat transfer agent (small coke at a temperature of 8500C and a gas with a free oxygen content of not more than 10 in flight at a temperature of 10500C) from cyclones 24, 29 forming part of the technological focus 2) and water gas reactor 11 respectively. In the first stage of the pryolyser 13, 160 kg of small coke and 32.5 kg of gaseous heat transfer agent are introduced. Coal pyrolysis ends at the temperature of 7800C in the second stage of pyrolyzer 19.

The excess gas is evacuated through the pipe 31, it is subjected to a purification and it is introduced into the energy unit. When the circulation of the small coke increases, it is introduced into the pyrolyzer in an amount of 203 kg, while the gaseous heat transfer agent is completely evacuated through the pipe 31.

 In the pyrolyzer, from 64.0 kg of dry coal and small circulating coke, 29.5 kg of gas and vapor mixture and 35.2 kg of small coke are obtained. The small coke is separated from the gas and vapor mixture and said mixture is sent to purification and to a condensation system.

 During pyrolysis and heating of coal, except small commercial coke, 18.0 kg of pyrolysis gas (pyrogas) are obtained 8.6 kg of resin and gasoline, 2.9 kg of water pyrolysis and the heat transfer agent.

The calorific value of the pyrolysis gas is 4840 kcal / m3 and it contains, in% by volume: C02-22,
CO-27, H2-20, CH4-21, hydrocarbons-10. In the pyrogas, 81,000 kcal, i.e. 23% of the potential heat of coal, are transferred, and in resin and gasoline, 67,500 kcal, i.e. 19% of the heat potential of coal. In the small coke (35.2 kg) which forms during the pyrolysis of the coal, 63% of the potential heat of the coal or 58% of the heat brought to the installation is transferred. It is possible to produce a variant according to which all of the semi-gas coming from the technological center 23 is introduced into the energy installation through the pipe 31 by increasing, in this case, the supply of the heat-transfer agent, of small coke , in the pyrolyzer about the same amount in kg.

 14.4 kg of small commercial coke, including 12 kg of carbon and 0.2 kg of hydrogen, are produced. 2.2 kg and 8.3 kg of small coke are transformed into gas and semi-gas in the second stage pyrolyser and in the technological center. With the small coke and the dairy products, 6.5 kg of ash contained in the fuel are eliminated.

The small coke heated to the temperature of 10500C in the technological furnace 23 is separated from the gaseous heat transfer agent and it is introduced into the reactor 11 of gas to water in which, from water vapor superheated in an amount of 18 kg and 166 kg of small powdery coke, 24 kg of water gas are obtained (during an H 2 O + C reaction). In cyclone 29, the gas in water is separated from the small coke (160 kg at a temperature of 8500C) it is discharged through line 32 and after cooling it is sent for purification and use in a energy unit and as a commercial product for obtaining hydrogen, a reducing gas or a synthesis gas.

The small coke, the heat transfer agent is brought through the hopper 30 into the pipe 14 in which it mixes with the gas (semi-gas) coming from the cyclone 24 and then this mixture is sent to the pyrolyser of the first stage to carry out pyrolysis, the cycle is closed the system presents the danger of harmful releases neither in its technological part nor in its energy part.

Example 2
This example illustrates an alternative embodiment of the process when the production of small commercial coke is not desired because of its high content of ash, sulfur and for other reasons. Transformation of the raw coal having the same composition as that indicated in Example 1 is carried out. In a gas-water reactor, a double quantity (36 kg) of water vapor is decomposed, evaporated from 100 kg. of coal and reacting with 12.6 kg of small coke. 48 kg of water gas, 8.5 kg of petrol and resin, 18.3 kg of pyrolysis gas, 3 kg of pyrogenic water, 6.5 kg of ash and slag, 105 kg of semi-gas. At this regime, all the humidity of the fuel used is gasified in an amount of 36 kg per 100 kg of coal, that is to say that it is transformed into gas in water. This directly saves about 6% of the heat of the starting coal by increasing the efficiency of transformation and use of the coal.

When there is insufficient steam in the case of possible variations in the practice of the degree of humidity and of the composition of the coal or in the case of a low carbon activity, through the pipe 28 is introduced from the outside adjustable amount of steam. The coal drying process can be carried out, if necessary (for construction reasons) without introduction of steam, that is to say only with introduction into the mill 2 of the solid heat transfer agent.

Example 3
This example illustrates an alternative embodiment of the process in which the small coke has a low activity of reaction with water vapor or a particular composition of the ashes. In this case, a high temperature of the heat transfer agent and small coke are brought into play which reacts with the water vapor.

 The transformation of coal is carried out: the organic substance of which has the same composition as that of Example I. The humidity of the coal is 27%, the ash content is o21. In a technological forum, air heated to the temperature of 7000C is introduced by the gas leaving the pipe 31 and the temperature is raised in the technological focus to 1500 to 16000C.

The ash is removed in the form of a liquid slag,
The product obtained is the same as that indicated in example 2; 36 kg of water gas, 6.4 kg of resin and gasoline, 13.7 kg of pyrolysis gas, 2.3 kg by volume of slag and 29.9 kg of ash. This makes it possible to transform all the coal into gaseous and liquid products while avoiding discharges of ash and sulfur oxides into the atmosphere.

Of course, various modifications can be made by those skilled in the art to the process which has just been described solely by way of nonlimiting example without departing from the scope of the invention.

Claims (5)

 1.- Process for thermal transformation of a ground solid fuel comprising a stage of drying of said fuel and its pyrolysis in two stages followed by a subsequent separation of the gaseous products and of vapors which form and of the small, caritized coke in that the drying of said fuel is carried out using a portion of said small hot coke at least a portion of the small remaining coke being subjected to additional heating at a temperature between 800 and 15000C by the gases and / or by burning partially the small coke, after which the small heated coke is separated from the gases and subjected to gasification by the steam obtained during the drying of said fuel, the gasification products which are formed then being separated from the small coke that then brought as heat transfer agent to the first stage of pyrolysis.  2.- Method according to claim 1, characterized in that a ground solid fuel is used whose particle sizes are not greater than 1.5  3.- Method according to claims 1 and 2, characterized in that one carries out the drying of said fuel in a stream of overheated water fear. 4.- Method according to claims 1, 2 and 3, characterized in that a portion of the gases separated from the small coke is brought to the first stage of pyrolysis. 5.- Method according to claim 4, characterized in that the gases brought to the first stage of pyrolysis contain only 2% by volume of free oxygen.