RU2437914C2 - Procedure for production of reducing gas from solid products of coal pyrolysis - Google Patents

Abstract

FIELD: gas and oil production.

SUBSTANCE: mixture for blowing preliminary heated to 700-850°C containing 70 wt % of steam and 30 wt % of oxygen is supplied under layer of solid product of coal pyrolysis - burning-hot coke. Produced reducing gas containing hydrogen and carbon oxide is withdrawn and used for preliminary blowing mixture heating.

EFFECT: raised intensity of output and reduced prime cost of reducing gas, decreased consumption of coke.

2 cl, 1 dwg

Description

The invention relates to the coke industry, in particular to the production of a reducing gas containing hydrogen and carbon monoxide, and can be used in gasification processes of hot coke.

A known method of producing a gas containing hydrogen and carbon monoxide by passing a mixture of hydrocarbon with water vapor through a coke layer [French patent No. 1380290, class. C10B, published on 10.19.64].

The disadvantages of this method are the large waste of coke from which the gas leaves, a decrease in the strength and particle size distribution of coke, a low yield of gas containing hydrogen and carbon monoxide.

The closest, in technical essence to the claimed method, is a method of dry quenching of coke and obtaining gases containing hydrogen and carbon monoxide, which includes cooling by passing a mixture of hydrocarbons with water vapor through a layer of coke, while the coke is preheated to a temperature of 1200-1300 ° C, it is cooled with a mixture of hydrocarbons with steam to a temperature of 700-750 ° C, and then they are cooled to a temperature of 200-250 ° C by passing an inert gas through a layer of coke, precede a mixture of hydrocarbons with steam linen is heated to a temperature of 700-750 ° C [USSR copyright certificate No. 802354, cl. СВВ 39/02, published on 02/07/81].

The disadvantages of this method include a decrease in the amount of coke (fumes) and quality deterioration due to the use of hot coke as a continuously moving packed material with a high temperature after it is dispensed from a coke oven (1000-1050 ° C), a mixture of coke and oxidizing is fed countercurrently to coke gases, as a result of heat exchange with coke, the temperature of the gas mixture rises and the coke oven gas is converted, while the endothermic conversion reaction takes away the heat of coke, cooling it, an insignificant yield reducing gas, additional fuel costs and cost increases due to raw materials in the form of high-calorific fuel - coke oven gas (the lowest heat of combustion of which is about 17,500 kJ / m ³ ), coke is the main product of production, therefore, its quantity and quality should not be reduced, and reducing gas is a minor product resulting from the conversion of coke oven gas, while the coke must be calcined before the conversion process to a temperature of 1200-1300 ° C.

The basis of the invention is the task of improving the method of producing reducing gas from solid products of coal pyrolysis, in which the heated mixture is supplied for blasting from below, under a layer of hot coke, the mixture for blasting is in the form of a mixture of water vapor and oxygen in a ratio of 70:30 (wt.% ), heated to a temperature of 700-850 ° C, provides an increase in the intensity of production of reducing gas, this ensures a reduction in fuel consumption, cost reduction, while the quality of coke is not reduced.

The problem is solved in that in the method for producing a reducing gas from solid products of coal pyrolysis containing hydrogen and carbon monoxide, which includes the supply of a preheated mixture for blasting through hot coke, according to the invention, the following differences are provided:

- the heated mixture for blasting is served from below, under a layer of hot coke;

- as a heated mixture for blowing serves a mixture of water vapor and oxygen in a ratio of 70:30 (wt.%);

- a mixture of water vapor and oxygen is preheated to a temperature of 700-850 ° C.

In addition, a mixture of water vapor and oxygen is heated with the resulting hot reducing gas.

The essence of the method is illustrated in the drawing, which shows a diagram of a device for performing the method.

A device for performing a method of producing reducing gas from solid products of coal pyrolysis contains a housing 1 with a device 2 for loading coke, a device 3 for supplying a mixture of water vapor and oxygen for blasting with tuyeres 4, a collector 5 for collecting and discharging the reducing gas installed above the reducing zone building 1, under the tuyeres 4, a furnace for collecting slag materials is installed, equipped with slots for liquid removal of slag from the device, a recuperator 6 for utilizing the heat of the reducing gas and heating a mixture of steam and oxygen.

The method is as follows.

Hot coke, coke loading device 2, is fed into the upper part of the casing 1, a mixture of water vapor and oxygen in the ratio (60-80): (20-40) wt.%, Pre-heated to a temperature of 700-850 ° C with the obtained hot reducing gas in recuperator 6, it is fed by device 3 from below, through tuyeres 4, under a layer of hot coke, while solid lumpy coke drops down as it burns out, towards a hot stream of a mixture of water vapor and oxygen, which, rising up, meets a layer of hot coke, at this gaseous x nomic reactants enter into chemical interaction with the carbon coke.

The claimed temperature range of 700-850 ° C is not simply a quantitative extension of the temperature range of heating the blast (600-750 ° C) in the zone of higher temperatures. Thus, the temperature fields in the reaction zones change, and consequently, the physical and physico-chemical phenomena in the process of gasification of carbon raw materials. So, in the lower (oxidative) zone, it is necessary that the coke carbon completely reacts with the oxygen of the blast by the reaction C + O ₂ → CO ₂ . Moreover, the reaction products can be adsorbed on the surface of the carbon body, since coke has a highly porous structure and is an excellent adsorbent of gases. The higher the degree of adsorption, the larger the surface of the carbon material occupied by the adsorbed molecules, and the less the possibility of carbon atoms to enter the oxidation reaction with oxygen with heat. The reaction considered above suggests that the reaction products are practically not adsorbed by the coke surface. Moreover, the higher the temperature in the combustion zone, the lower the degree of adsorption, the higher the thermal effect of the combustion reaction, which is a consequence of a higher rate of the chemical reaction of combustion and a more complete reaction of carbon with oxygen. Thus, the present invention most fully realizes the thermal and material potential of coke in the oxidation zone of the gasifier.

The coke gasification process is a heterogeneous process. Providing high temperature in the reaction zone, large values of the reaction rate coefficient (which is determined by the Arrhenius equation:

k = A * e ^{-E / RT} ,

where A is the reaction rate constant,

E is the activation energy,

R is the specific gas constant,

T is the temperature of the process, K.

Those. the higher the process temperature (T), the greater the reaction rate coefficient (k).

Therefore, in the oxidizing zone, the combustion reaction of coke carbon occurs at a higher rate, and in the reduction zone, the reaction of reduction of CO ₂ to CO and H ₂ O to H ₂ takes place. Moreover, at higher temperatures, there is a significant reaction for the conversion of carbon monoxide and water vapor: СО + Н ₂ О↔H ₂ + СО ₂ , which is significant for the overall balance of the gasification process, which leads to an increase in the concentration of hydrogen in the reducing gas. Moreover, with increasing temperatures, the equilibrium, according to the Le Chatelier principle, shifts towards the formation of hydrogen, i.e. direct reaction amplifies. Similarly, the effect of temperature on reversible reactions: СО ₂ + С↔2СО, С + Н ₂ О↔Н ₂ + СО, etc., taking place in the vapor-oxygen gasification of coke.

And you can increase the temperature in the gasifier only in three ways:

1) by preheating the blast to certain temperatures,

2) by changing the composition of the blast in the direction of enrichment with oxygen,

3) by reducing the heat transfer of the gasifier to the environment.

The third way is not considered by the authors, because This is a purely technical technique.

But the first two ways are implemented in the application for an invention and a method for their implementation is proposed.

The question “to what temperature should the blast be heated” is not a quantitative sign. Temperatures of 600-750 ° C make sense for the maximum conversion of carbon dioxide and water vapor by coke according to the reactions:

С + Н ₂ О ↔ Н ₂ + СО

CO ₂ + C ↔ 2CO

But, at the same time, it is necessary to perform another important function - to cool the coke with minimal waste, i.e. maximize coke yield. Experimentally and analytically, the optimal temperature range for this process was determined to be 600-750 ° C, because at temperatures below 600 ° C, the conversion process attenuates sharply, and at temperatures above 750 ° C the coke burn in the dry quenching unit is enhanced. At the same time, the yield of CH ₄ in the composition of the reducing gas increases, which is undesirable for synthesis gas.

In the proposed method, as a result of using a different temperature range for heating the blast and a different composition of the blast, a completely different method of gasification is implemented, including for another purpose: maximize the use of the carbon resource in gasified coke, i.e. completely transfer it to a gaseous state. It is for this purpose that oxygen is introduced into the blast, which ensures the presence of an oxidizing zone in the gasifier with heat coming from the carbon oxidation reaction and an additional heat coming from reactions from the preliminary heating of the blast. Heating the blast to temperatures of 600-750 ° C does not provide high-temperature oxidation and reduction zones in the gasifier and shifts the reversible reduction reactions of carbon dioxide and water vapor towards the starting substances, and also does not provide complete gasification of coke solid carbon to CO ₂ , which leads to increased mechanical entrainment of carbon coke. Raising the temperature of the blast to 850 ° C ensures the ability to maintain temperatures in the oxidation zone at the level of 1200-1350 ° C, which is optimal for the coke gasification process. The gas temperature at the outlet of the gasifier is sufficient to heat the source blast in the heat exchanger (for example, shell-and-tube) to 850 ° C. Heating the blast to temperatures above 850 ° C by utilizing the heat of the exhaust gas is very problematic technically and economically unprofitable due to the low driving force of heat transfer at the outlet of the heat exchanger.

We believe that the temperature range chosen for the formula of the invention is technically and technologically justified by us, as it allows us to organize a qualitatively new gasification process to produce a new product.

Free oxygen is present in the lower part of the hot coke layer, therefore, the main chemical reaction will be the combustion of carbon coke

C + O ₂ → CO ₂ ↑.

During the reaction, carbon dioxide is formed - the product of the complete combustion of coke carbon, which is contained in a significant amount in the lower part of the layer of hot coke, this zone is considered to be oxidative, the carbon dioxide formed in it rises and is restored by the hot coke carbon by the reaction

CO ₂ + C → CO ↑ + H ₂ ↑.

The oxidizing and reducing zones are combined into a gasification zone.

The temperature developing in the combustion zone is higher than the melting temperature of the ash components of coke; therefore, liquid slag removal occurs.

The reducing gas resulting from these reactions is collected in a collector 5, and then taken to a recuperator 6, where its heat is utilized to heat the blast mixture, and the cooled reducing gas is supplied for further use.

An example of the method.

Hot coke with a temperature of about 1000 ° C is fed to the upper part of the device body 1, a blast mixture consisting of water vapor and oxygen, preheated in heat exchanger 6 to a temperature of 850 ° C, comes from below, under a layer of hot coke, while the oxygen content in the mixture is 30%, solid lumpy coke as it burns down to the hot steam-gas stream, which, rising up, meets the lower layer of hot coke, where there is free oxygen, gaseous chemical reagent chemically react with carbon coke formed while carbon dioxide is directed upward and is restored hot coke carbon. The reducing gas leaving the collector 5 consists of carbon monoxide (CO) 65%, hydrogen (H ₂ ) 33%, methane (CH ₄ ) 0.3%, and the outlet gas temperature is 950 ° C. The consumption of water vapor per 1 m ^{3 of the} resulting reducing gas is 0.620 kg, and technical oxygen (in terms of 98% concentration) is 0.150 kg.

The temperature developing in the combustion zone reaches 1350 ° C, it is a higher temperature than the melting temperature of the ash components of coke, comprising 1300 ° C, while liquid slag removal occurs.

The average specific productivity of the device for performing the method of 1500 m ³ / nm ² hours, the efficiency reaches 92%.

The performance of the method of producing reducing gas from red-hot coke is given in the table.

The performance of the method of obtaining reducing gas The oxygen concentration in the dry blast,% thirty The gas content,% With 35 H ₂ 63 CH ₄ 0.3 The heat of combustion of gas (lower), kJ / m ³ 11770 Gasification efficiency,% 92 Costs per 1 nm ³ gas: - coke, kg / m ³ 0.210 - water vapor, kg / m ³ 0.620 - technical oxygen (98%), kg / m ³ 0, 15 The temperature of the reducing gas at the outlet of the gas generator, ° C 950

When performing the proposed method above the gasification zone, there is no fuel preparation zone consisting of semi-coking and drying zones, therefore, the temperature of the loaded coke excludes moisture in the initial fuel, and the pyrolysis stage is performed in coke ovens.

Thus, secondary processes are excluded from the gasification process, the time from loading to the start of gasification of fuel is reduced, therefore, the process is intensified, in addition, the products of dry distillation are not mixed with the gas formed in the gasification zone, because they are absent in the proposed method, therefore, the practical composition of the gas is equal to the theoretical.

The proposed method of gasification involves slag removal from the device in a liquid state with subsequent utilization of slag heat.

Given the temperature level reaching 1350 ° С and more, it becomes possible to gasify any type of coke, regardless of the melting ash and coke fineness class, which is typical for bulk coke, while the specific consumption of water vapor to produce 1 m ^{3 of a} mixture of CO + H ₂ s liquid slag removal lower than during gasification with solid slag removal.

As secondary products in the proposed method, you can get a wide range of useful substances, such as granular slag, raw materials for slag wool, cement, various types of casting from stone, etc.

Thus, the proposed method for producing reducing gas from solid pyrolysis products, using hot coke as carbon raw materials and fuel, has the following advantages over the prototype:

- due to high temperatures in the recovery zone (up to 1000 ° C), favorable conditions are created for the recovery of carbon dioxide and water vapor, the average productivity reaches 1500 m ³ / nm ² hours, instead of 400-500 m ³ / nm ² hours (according to the prototype) , in addition, due to better conditions for the occurrence of reduction reactions, the heat of combustion increases by 1250-2100 kJ / m ³ while increasing the efficiency of gasification to 92%;

thermodynamic efficiency in the proposed method is much higher, because high-calorie gas is used for conversion, and a less deficient mixture of water vapor and oxygen is used as a mixture for blasting;

- in the process of obtaining a reducing gas, high temperatures are achieved in the oxidation zone, because the blast mixture is preheated in the recuperator by the off-gas gas, while the heat of the gaseous product is utilized, thereby increasing the efficiency of the method for producing the reducing gas.

As studies have shown, heating the mixture for blasting to 850 ° C increases the calorific value of gas to 1000-1400 kJ / m ³ ;

- significant intensification of the process in connection with the continuous removal of slag from the reaction surface during liquid slag removal, because the temperature in the oxidation zone reaches 1350 ° C or more, which improves the diffusion conditions of gas reagents in the oxygen zone.

Claims (2)

1. A method of producing a reducing gas from solid products of coal pyrolysis containing hydrogen and carbon monoxide, which comprises supplying a preheated mixture for blasting through hot coke, characterized in that the preheated mixture for blasting is passed from below under a layer of hot coke, and as heated mixture for blast serves a mixture of water vapor and oxygen in the ratio, wt.%: 70:30, preheated to a temperature of 700-850 ° C. 2. The method according to claim 1, characterized in that the mixture of water vapor and oxygen is heated with the obtained hot reducing gas.

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