JPS6236079B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a two-step process for converting solid particulate carbonizable material into synthesis gas and charcoal byproducts. The first stage involves relatively low temperature pyrolysis of the carbonizable material and the second stage involves partial oxidation of the plurality of volatiles generated during the pyrolysis. Coal and lignite, which are widely available at reasonable prices and in near-inexhaustible quantities, have long been recognized as powerful sources of liquid and gaseous fuels, including what is known as syngas. There has been a considerable degree of interest for generations in the conversion of these materials into synthesis gas, and interest in synthesis gas programs has increased as the cost and availability of alternative sources such as methane and naphtha and the demand for synthesis gas has increased. and the amount of research funding increased or decreased. Suffice it to say that there is a wealth of scientific literature suggesting methods for converting coal to syngas. A huge number of engineering obstacles have hindered the development of this technology. The widely available carbonizable materials, i.e. coal, lignite, peat and wood, are heterogeneous materials containing large proportions of substances that can be volatilized by pyrolysis and the gases generated vary depending on the source material. It encompasses a wide range of organic compounds consisting of significant amounts of sulfur-containing, nitrogen-containing, and oxygen-containing compounds. Non-volatile residues, such as coke, contain carbon and ash and often nitrogen and sulfur. In summary, bituminous coal, subbituminous coal,
Lignite and wood etc. are all difficult raw materials. When devising a method for the conversion of solid carbonizable material to synthesis gas, the immediate concern of the process engineer is as to what proportions the feedstock should be converted to gaseous products, principally synthesis gas and impurities, and, incidentally, There is a need to make a choice as to what proportion should remain as a solid by-product. This solid by-product is ash, slag, coke or charcoal. Furthermore, it can be appreciated that complete or substantially complete conversion of solid carbonizable material to synthesis gas is an attractive idea. The economic and engineering parameters are uncomplicated in that the entire production unit is designed and located approximately based on the syngas market, and the production equipment designer and Release the operator. Indeed, much of the prior art has developed products in the direction of complete conversion to syngas. Parallel to this syngas development, there have been many years of efforts by those skilled in the art to convert as-mined coal, especially bituminous coal, into relatively valuable solid products such as coke or clean desulphurized coal or charcoal. It has been done. If the objective of the process is a value-added solid product, any material volatilized by this conversion process will be a by-product that can be treated in some way. In some cases, the volatiles have been consumed to substantially meet the thermal requirements of the process, such as the old beehive coke oven process of making coke. Many researchers in the industry, like this inventor,
Efforts were made to provide an economical coal conversion method that produces both synthesis gas as well as valuable residual coal. It is believed that the process of the present invention has a number of advantages over previously available conversion methods. Briefly, it is an object of the present invention to provide both relatively clean gas products and superior charcoal products from solid particulate carbonizable materials. The term carbonizable is used herein as a general term for carbonaceous materials that thermally decompose into char or coke with the evolution of volatile components. Typical carbonizable materials are wood, peat, lignite, and all coals except anthracite. The combustion of high sulfur coal was met with ever-increasing unpopularity due to numerous and noisy objections to oxidized sulfur in stack gases. A common objection has been raised to the combustion of high nitrogen content coal. This is because its combustion releases nitrogen oxides into the stack gas. low sulfur,
There are great expectations for low nitrogen steam coal. However, at the same time sufficient amounts of high sulfur and high nitrogen coal are available. An economical method of converting high sulfur coal and/or high nitrogen coal, lignite, etc. to low sulfur, low nitrogen combustible coal would be clearly advantageous. Therefore, thermally efficient methods of converting all or a portion of these materials into relatively clean synthesis gas would also be advantageous. A process for the total conversion of coal with high thermal efficiency, partially to low sulfur and low nitrogen and partially to relatively clean syngas, would meet this unmet need in the technology. In summary, the process of the present invention involves the first step of contacting the crushed or pulverized solid carbonizable material, preferably dried and preheated to 300°C, to hot recycled synthesis gas, and thus at a temperature of about 500 to 1000°C. It is a two-step process that heats the incoming material to a range of pyrolysis temperatures. The carbonizable material may be at least partially devolatilized to selectively remove sulfur and nitrogen from the coal in which the devolatilization occurs. The degree of devolatilization that can be achieved depends, of course, on the material being pyrolyzed, the pyrolysis temperature and the treatment time. Although substantially complete devolatilization is obtained by the practice of the present invention, the carbonizable material need not be completely devolatilized to become a coke product.
Typically, this material is a charcoal that retains up to about 20% volatile matter and therefore retains some of the combustible properties of the feedstock. The thermal energy is recovered from the hot coal product at 500 to 1000°C and used to dry and preheat the incoming solid carbonizable material as required, thus improving the thermal efficiency of the process as a whole. do. In the second stage of the process, the vapor phase mixture of recycle gas and generated volatiles is heated to a temperature of about 1000 to 1500°C.
is partially oxidized at temperatures in the range of 100 to 100%, yielding gases with high concentrations of hot hydrogen and carbon monoxide, especially when the partial oxidation is carried out with commercially available pure oxygen. This gaseous product is naturally free of tar, phenols and other macromolecular components. This gas is then fairly pure synthesis gas. A portion of this syngas is removed as a product of the process and the remainder is used as hot recycle gas to pyrolyze the incoming solid carbonizable material. For a further understanding of the invention, reference is made to the accompanying drawings, which illustrate the method of the invention in block diagram form. Referring to the accompanying drawings, a stream of solid particulate carbonizable material entering via tube 11 and preferably dried and preheated and a stream of hot recycle gas from tube 12 are introduced into a pyrolysis device 10. Inside the pyrolysis device 10, the granular material is heated to a range of 500 to 1000°C, pyrolyzed and carbonized, releasing some volatiles that can be liberated from the fuel material, but inevitably Don't release everything. For convenience, the accompanying drawings show a combined steam and charcoal outlet from the pyrolysis device 10 as from a tubular pyrolysis device. Produced charcoal is removed from gas-solids separator 20 in line 13, while a vapor phase mixture of slightly cooled recycle gas and generated volatiles is passed from separator 20 via line 14 to partial oxidizer 30. pass. A stream of oxygen, preferably commercially available pure oxygen, introduced into partial oxidizer 30 from tube 15 partially combusts the vapor mixture inside partial oxidizer 30 and
The temperature of the partial combustion products is raised above 100°C, generally in the range of 1000 to 1500°C. The hot partial combustion products exiting the partial oxidizer via line 16 exit through line 17 as a recycle stream which flows back to the pyrolysis unit 10 via line 12 and as the (hot) synthesis gas product of the process. Divided into vapor products. Although not shown in the block diagram of the accompanying drawings, it is noted that it is optional that the carbonizable solid material used in this method is first dried and preheated, and that this measure saves considerable thermal energy. be able to. Also, although not shown, sensible heat is recovered from the hot gas products. Needless to say, gas at 1000 to 1500°C can generate steam for power generation and/or
In overpressure conditions, a turbine can be passed to generate electrical energy. The method of the invention therefore constitutes a combination of two processing steps that operate almost independently, but are nevertheless coupled together. The first stage is pyrolysis of the carbonizable material by direct heat exchange with hot reducing gas. The pressures, temperatures and proportions of those gases can be as desired. Although the gas contains oxygenated compounds such as carbon monoxide, it is believed that this gas also contains hydrogen and is an overall reducing gas and therefore has some advantage for this material undergoing thermal decomposition. The reducing gas is applied. Endothermic reactions that reduce coal yield, such as steam coal reactions and carbon dioxide reactions, are suppressed. Hydrogenation reactions such as desulfurization and denitrification reactions are facilitated. As a result, for some carbonizable materials, such as some bituminous coals, the product of the coal is reduced in sulfur and/or nitrogen content relative to the feedstock. The selection of particular pyrolysis conditions, such as temperature and reaction time, suitable to enhance desulfurization and/or denitrification of a particular feedstock is considered to be within the practice of this invention. First, let's consider the desulfurization aspect of this method. It is known to those skilled in the art that pyrolysis of coal in the presence of syngas or alternatively in the presence of any reducing or inert sweep gas removes sulfur from coal (e.g. U.S. Pat. No. 4,118,201). reference). The hot recycle gas used here is approximately 1:2 to 2
Contains carbon monoxide and hydrogen in proportions that can be adjusted within a 1:1 range. The vapor content of this synthesis gas product is usually about 10% by volume, but can be increased to 40% by volume, for example, if desired. The pyrolysis temperature can be adjusted by controlling the temperature and amount of recycle gas. Furthermore, the pressure at which the pyrolysis is carried out can be varied within a wide range. Sulfur-containing feed materials that can be carbonized by treatment with a reducing sweep gas at overall pyrolysis temperatures can be desulfurized to a sufficient degree to the extent that such materials meet the conditions to achieve high levels of desulfurization. In the practice of the present invention, it can be thermally decomposed. The pyrolysis stage of the present invention is relatively flexible such that pyrolysis conditions consistent with significant reduction of the sulfur content of the charcoal product are readily available. To reiterate, the hot recycle gas used in pyrolysis is a reducing gas. The combined hydrogen and carbon monoxide of this hot recycle gas typically exceeds about 50% by volume. The product gas and therefore recycle gas compositions mentioned in the following examples have concentrations of hydrogen sulfide ranging from 1 to 3% by volume, H ₂ S/H ₂ volume ratios of magnitude up to 0.06, and 0.01 to 3% by volume. _H2S /( _H2S) in the range 0.03
+CO) volume ratio. These values depend on the amount of sulfur in the feed, the amount and composition of volatiles formed, and the degree of desulfurization of the charcoal. It is known to those skilled in the art that the presence of _H2S in the recycle gas tends to inhibit desulphurization of the coal, especially if the ash content of the coal contains significant amounts of iron or calcium ( For example, British patent no.
No. 1495997). For example, for low desulfurization of coal from high sulfur coal (less than 1% by weight of this coal),
Means that do not involve pyrolysis conditions can be used, such as removing ash from the feed (eg, by floatsink techniques) or incorporating a hot hydrogen sulfide gas removal device in a recirculating gas circuit. The details of such additional machining are outside the scope of this invention. Dry bituminous coal, regardless of class, typically contains 1 nitrogen.
It contains from 1.5% by weight. Environmental concerns regarding nitric oxide (NOx) emissions require limits on these types of emissions. from chimney gas
Although NOx purification or careful control over combustion conditions to minimize stack gas NOx is a suggested measure, this reduction in the amount of nitrogen in the fuel has many implications for power plant operators. Provide advantages. Unfortunately, standard physical coal purifiers used heretofore are not capable of selectively removing nitrogen. It is not certain that pyrolysis of coal in the presence of inert gas at temperatures below about 1000°C can selectively remove nitrogen from the coal. However, pyrolysis in the presence of hydrogen, as performed by the practice of the present invention, has been reported to selectively remove nitrogen. Overall, this pyrolysis step is carried out to produce a charcoal product that is valuable for steam coal purposes. In particular, there is no need to strive to remove the maximum proportion of volatiles from the carbonizable material. In practice, the charcoal may contain up to about 20% volatile matter.
In the practice of the present invention, emphasis is placed on the nature of the material volatilized from the carbonizable feedstock and on the nature of the char product rather than on the amount theoretically removed. Thus, nearly any carbonizable material up to intermediate volatile content bituminous coal can be used in the practice of the present invention. The pyrolysis reactor can be an entrained flow reactor, a liquid bed reactor, or any other continuous device capable of devolatilizing coal by pyrolysis carried out by contact with heated reflux gas. Details of the equipment used for pyrolysis do not form part of this invention. The gas removed from the pyrolyzed feedstock is
It includes significant cooling recycle gas added along with the vapor phase material volatilized from the feed. Thermal analysis of the carbonizable feed to char volatilizes more organic combustion material than is consumed in the partial combustion stage, and as such is an essential aspect of the process. As already pointed out, vapor phase flow
and 1500° C., preferably in a partial oxidizer 30 with commercially available pure oxygen. The products of this partial combustion are hydrogen and carbon monoxide-rich gases substantially free of such things as tar, phenols, or other undesirable polymeric components. Phenol is destroyed within seconds at temperatures above about 1000°C. The partial oxidation is carried out under an environment suitable for consuming the polymeric components volatilized by thermal decomposition. Therefore, the proportion of oxygen is controlled and the combustion conditions are controlled to produce a high temperature and relatively clean synthesis gas.
A portion of this synthesis gas is removed as a product of the process and the remainder is recycled to the pyrolysis stage. The pressure of this oxidation step should approach the pressure of pyrolysis and is about 3.5 Kg with a preferred range of about 7.03 Kg/ ^cm2 Gauge (100 psig) to about 21.9 Kg/ ^cm2 Gauge (33 psig). / ^cm2 gauge pressure (50 psig) to about 70.3 kg/ ^cm2 gauge pressure (1000 psig). While operating at overpressure minimizes downstream gas compression demands for this gas user, operating at pressures higher than the preferred range complicates solids feed equipment and increases the risk of excessive hydrogasification of coal and resulting in methane formation. In the operating temperature range of the oxidation stage, NH ₃ , NCH,
It is believed that nitrogen is converted first to _N2 and sulfur is converted first to _H2S , although small amounts of compounds such as COS, and Cs are possible. Particularly when maximum coal desulfurization is not a requirement, sulfur compounds may be left in the recycle gas and those sulfur compounds removed from the product gas by known methods such as washing hot carbonic acid solutions after cooling. You may. Alternatively, the high temperature desulfurization device may be used directly in the recirculation gas circuit. The hot recycle gas stream is driven, for example, by injecting oxygen and/or steam from a pressure source above the pressure of the pyrolysis and oxidation stages. As already pointed out, a desirable feature of the present invention is that its thermal analysis and synthesis gas production are carried out almost independently of each other, and that the desired results from each stage are
That is, each step is carried out under conditions suitable for producing high quality coal with some sulfur and/or nitrogen removed from the produced coal and for producing synthesis gas free of high molecular weight organic compounds. Simply put, the quality of both by-products can be controlled separately. The practice of the invention may include steam injection as a suspending medium for the incoming carbonizable material, for example just before or after partial combustion, or just before the contact of the hot recycle gas with the feed, or as another example, the caking of coal. Optionally, some measures may even be included which are particularly useful in one or both stages and are therefore not detrimental to the quality of the product, such as preheating the coal so as to reduce its tendency to burn. Although originally these two stages are operated independently, they of course form an integral whole in a thermal sense. Both stages collectively offer significant thermal advantages to the method. The charcoal is
It is released at relatively low temperatures, ie below 1000° C., and in addition the sensible heat of the charcoal can be recovered, for example to dry and preheat the feedstock. The gas product stream is generated as a relatively clean, hot synthesis gas, a condition that facilitates the recovery of the sensible heat of this gas, for example, by the generation of electrical energy. This high thermal efficiency resulting from the production of hot gas products and cold solid products by the method of the present invention
This two-step process can reduce the amount of oxygen required per unit weight (or volume) of syngas product and/or increase the yield of charcoal and/or, alternatively, reduce some volatilization of the charcoal. This can be demonstrated in a variety of ways, including in particular being able to retain components. All of these aspects are due to the absence of molecular oxygen in the pyrolysis stage, the high concentration of reducing gases in the pyrolysis stage, and the virtual completeness of tars, phenols, and hydrocarbons generated from the material undergoing carbonization during partial oxidation. Generally attributed to destruction. These components are converted to carbon monoxide and hydrogen. For a better understanding of the invention, reference is made to the following examples.

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[Table] 1st to 6th Examples These examples are to some extent based on the 6th example of Illinois
This paper is based on data from thermodynamic calculations made from the pyrolysis of bituminous coal and to some extent to predict the performance of partial oxidation. The first and second embodiments are
The promising performance of single-stage oxidative pyrolysis at 1000°C using commercially available pure oxygen is shown. Partial combustion is
Used as a heat source for pyrolysis. In the first embodiment, the combustion selectively consumes the products of charcoal;
In embodiments, combustion consumes the generated steam products and converts the combustion products, thus balancing them in a methanation process. The third to sixth embodiments illustrate implementation of the present invention. While the third example shows the effect of pyrolyzing charcoal at 200°C, it shows the effect of steam oxidation at 1000°C. The fourth example operates the pyrolysis at 500°C. Coal was 205℃ for the fifth example.
is preheated to a temperature of 100°C before contacting the hot recycle gas.
The sixth example shows the effectiveness of steam addition to control partial oxidation. The purpose of steam addition can be varied to drive the recycle gas stream, modify the hydrogen to carbon monoxide ratio of the syngas product, and reduce the potential for carbon precipitation. The results of these six examples show that the mass balance (first
Table), enthalpy equilibrium (Table 2) and product yield (Table 3) are displayed below. As can be seen from Tables 1, 2 and 3 above, meeting the heat demand for pyrolysis through the combustion of solid carbon as in the first example is the same through the combustion of the volatile products. It requires more oxygen (approximately 28% or more) to provide energy and meet the heat demand for pyrolysis. The corollary of this difference is that the conditions of the first embodiment produce less char product and more tar, oils, and product gases than the conditions of the second embodiment. The working conditions of the second embodiment are relatively large amounts of syngas (per unit of oxygen and solid fuel consumed).
Create. The second embodiment is more suitable for comparison to the practice of the invention than the first embodiment, since tar and oil are the materials that are combusted to meet the thermal demands for the practice of the invention. Comparing the results from the second example against the results from the third example, the oxygen demand is observed to be slightly more favorable to the two-step process of the present invention. Both processes produce only charcoal and gas products. However, the two-step method of the present invention provides approximately
Produces more than 10% charcoal product and therefore less than about 10% gas product. A relatively high proportion of net product is therefore obtained in the form of charcoal. The consumption rate of oxygen and solid fuel per unit of syngas product is reduced. As can be seen by comparing the weight balances of the third and fourth examples, the pyrolysis stage is relatively low temperature but results in a slight increase in the consumption rate of oxygen and solid fuel per unit of syngas product. If operated sacrificially, a considerable reduction in oxygen consumption is obtained. For example, the mass balance for the fifth embodiment, which uses sensible heat from the product coal to preheat the coal, is such that its oxygen demand is therefore reduced somewhat further.
It has been demonstrated that the consumption rate of oxygen and solid fuel per unit of syngas product is further reduced. As shown by the data of the sixth example,
Steam addition changes the hydrogen to carbon monoxide ratio of the product gas and has no material impact on coal and oxygen usage. As can be seen from the product yield information in Table 3, the product gases resulting from the practice of this invention are almost entirely hydrogen and carbon monoxide. Some of the advantageous results obtained by practicing the present invention are not clearly explained by the data presented in Tables 1, 2 and 3 above. Therefore, the volatile retention of charcoal (expressed in product yield, Table 3) is an advantage. This makes the coal even more desirable for boiler fuel purposes. Compared to some proposed devices, the pyrolysis of the present process operates at relatively low temperatures, thus reducing the sensible heat of the charcoal product and generally promoting increased thermal efficiency. The relatively high temperature of the synthesis gas due to partial combustion of the synthesis gas in accordance with the practice of the present invention enhances the conversion of methane to hydrogen and carbon monoxide and reduces the content of this particular component in the product gas to very low levels.
Recovery of sensible heat from the product gas is of course considered.

[Brief explanation of the drawing]

The accompanying drawings are block diagrams of preferred embodiments of the method according to the invention. 10...Pyrolysis device, 11, 12, 13, 1
4, 15, 16, 17... tube, 20... separator,
30... Partial oxidizer.

Claims (1)

[Claims] 1. (a) By contacting carbonizable solid particulate material with hot recycle gas,
pyrolysis at a temperature of 1000°C to 1500°C and then separating the resulting char from a vapor phase mixture of recycle gas and volatiles derived from the carbonizable material; (b) heating the vapor phase mixture to a temperature of 1000°C to 1500°C; (c) using a portion of the gas from the partial oxidation as a hot recycle gas to pyrolyze the carbonizable material and removing the remaining gas. A method of converting materials into charcoal and synthesis gas. 2. A process according to claim 1, characterized in that a partial oxidation is carried out with commercially available paper pure oxygen, thereby obtaining a relatively pure synthesis gas. 3. Process according to claim 1, characterized in that steam is added to the vapor phase mixture of the recycle gas and volatiles derived from carbonizable material. 4. Process according to claim 1, characterized in that the carbonizable material is preheated before pyrolysis. 5 Pyrolyzing the carbonizable material under hydrodesulfurization conditions,
A method according to claim 1, characterized in that the sulfur content of the charcoal is thereby reduced. 6. Process according to claim 1, characterized in that the pyrolysis is carried out at 700 DEG C. to 1000 DEG C. under denitrifying conditions, thereby reducing the nitrogen content of the charcoal. 7. The method according to claim 1, characterized in that the thermal decomposition and partial oxidation are carried out under pressure conditions exceeding atmospheric pressure. 8. Process according to claim 1, characterized in that the sum of hydrogen and carbon monoxide in the hot recycle gas exceeds 50% by volume.