DE2327008A1 - PRODUCTION OF GAS FROM COAL - Google Patents

Description

United States Atomic Energy Commission, Washington, D.C. UNITED STATES.

Production of gas from coal

The invention relates to a method for producing gas from an underground coal store for the production of synthetic natural gas.

The economy in the United States. And in other countries is faced with the constantly dwindling reserves of domestic energy sources, such as the reserves of crude oil and natural gas. The shortage of natural gas or natural gas is increasing, so that more and more imports are required or it becomes necessary to produce synthetic natural gas by using coal or other coal mined in large factories imported petroleum components gasified. In any case, the cost of such an energy source is many times that

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Costs for the natural gas or natural gas that were previously available. The major cost components of the gas produced by surface gasworks are the production costs and the costs for that Gasworks itself. It is well known that extraction costs rise very sharply when deeper coal deposits are exploited should, in place of the coal deposits to be mined in the opencast mine. In doing so, there are also various problems related to environmental pollution in such gasworks, with particular emphasis on sulfur removal and contamination by fly ash and waste disposal is to be considered.

Attempts have been made since the middle of the 19th century to generate fuel gas by exploiting a coal store by in-situ gasification processes (see for example "The Chemistry of Coal Utilization", Supplemental Volume 1968, J. Wylie Press, Chapter 21, Editor: Homer Lowery). Most of these attempts have been directed to shallow deposits of subbituminous coal in eastern Germany, in Russia in the Moscow area, and in Alabama (conducted by the US Bureau of Mines). In these methods, air at approximately atmospheric pressure is pumped down into an opening and passed over one or more burning coal stores, whereupon the air is collected in another hole. These holes have different shapes, but in any case most of the carbon in the CO has been converted, with just enough left over H ₉ and CO, to produce a fuel gas of a very low quality. Such gases typically have calorific values of 100 to 300 BTU / cubic foot, while pure methane (natural gas) has a calorific value of approximately 1000 BTU / cubic foot and is suitable for economical pipeline distribution. Analyzes of the burn zones were carried out by means of tunnels running parallel to these zones and connected to them by small horizontal drill holes; the results indicated that most of the CH and a substantial portion of H ₀ and CO are burned near the exit zone. This occurs because the inlet air passes the hot combustion front or zone and reacts with the outlet gases, consuming most of the gas. Nonetheless, establishments operating by this method became continuous

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operated for the past 40 years, with a gas lower • Quality was produced from coal that would otherwise not be usable due to its high ash content.

Similar procedures do not apply to deep coal reserves practicable, since the costs for the installation of pipes and the formation of the required tunnels would be too high. Even the gas would be of such low quality and caloric value that the transport could get through Pipelines could not be carried out economically.

The invention now aims to provide a method by means of which such coal bearings are economically converted into a fuel gas ,, i.e. a synthetic natural gas or natural gas converted economically can be. -

To practice the present invention, a relatively thick and deep coal store is selected, which one Has a thickness or composite thickness of at least 50 feet and is well below the water table. By any suitable means will break a large volume fraction of the bearing. From an economic point of view Breaking by explosives is generally preferred because the explosives are properly spaced through boreholes can be brought in. In addition, selected boreholes can be provided with suitable formwork, which act as reactant inlet lines are usable. The product outlet lines can be provided in the form of boreholes, which made by incline drilling processes and extending from the surface to the lowest broken pieces. By using suitable formwork, for example with perforated lower ends, the generated gas can flow to the surface a processing plant. In some cases can the output line through a suitably arranged shaft with radially running channels (galleries). ,

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At the beginning of the work, a mixture of oxygen and a fuel gas is introduced through the reactant inlet lines and ignited so as to open the upper layer of the divided coal Reaction, i.e. bringing it up to ignition temperature. Generally the output lines are terminated at this point, so that in the cavity formed by the divided material volume a pressure up to an operating range in the Can build on the order of 500 to 1000 psi. The operating pressure can be selected to match the hydrostatic Groundwater pressure is in equilibrium, so that no water enters and at the same time the hydrostatic pressure leaks of the cavity eliminated or minimized. In addition, increased pressure promotes methanation reactions in the crushed Coal layer, so that a gas with a high calorimetric value results.

When the desired operating pressure is reached, the gas or product outlet lines are opened and reaction water is introduced in a suitable form together with oxygen in order to come into contact with the ignited upper layer of coal. The withdrawal of the product gas is then regulated according to the reactant inlet in order to maintain the operating pressure. Thereupon, the inflamed location spreads downwardly from, with a temperature in the range of about 600 ⁰ K to 1500 ° K, preferably in the range of about 650 1100 ⁰ K, where this development is going on, when the water and the oxygen react with the upper layer of coal. The heat carried along by the flowing reaction gases heats the layer below the hot layer zone to a temperature which is lower than that in the hot zone, as a result of which methane-generating reactions occur there. It should be noted that the use of a downward progressing reaction ensures a stable burning or reaction zone that eliminates dan "bypassing. As a result of the above-mentioned reactions a gas is produced which contains methane, water vapor, possibly CO and H ₂ and also CO ₀ The C0 _o gas can be removed and the water vapor is condensed in a device on the earth's surface,

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while - if desired - CO and H ^ catalyze the reaction be brought to produce methane. In either case, you get a high calorie gas that is used as fuel and can be used in chemical syntheses.

In the method according to the invention, it is advantageous that on the No ash is produced on the surface of the earth, and that no other ash is produced either Debris heaps arise. It also eliminates the cost of extraction and the cost of those required on the surface Factory facilities are drastically reduced as there are no large reaction facilities and converter are required.

The inventive method makes the in-situ gasification of deep-lying coal deposits using elevated pressures and Temperatures possible.

In addition, reference should be made at this point to the following literature on the prior art: "Les applications de 1'explosion thermonucleaire" by Camille Rougeron, Editions Berger-Levrault, Paris _r 1956.

Further advantages, objectives and details of the invention emerge from the following description with reference to the drawing; in the drawing shows:

Fig. 1 is a cross-section of a subterranean formation with a relatively thick coal bed, soft for use in accordance with the invention suitable is;

2 shows a representation of a blast hole pattern for the introduction an explosive for vibrating the coal store shown in Fig. 1;

Fig. 3 is a schematic representation of the gasification of the coal serving factory arrangement;

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FIG. 4 is an enlarged view of the split coal deposit of FIG. 3, along with a temperature profile and the occurring in the various parts of the reaction zone Reactions.

Coal deposits are widely distributed across the North American continent and the rest of the world. For the purposes of the present In the invention, coal deposits between approximately 600 and 3000 feet below the surface are of particular interest. The western states of the USA are particularly rich with coal deposits blessed what appropriate physical and chemical

1 have 2 properties. Estimated 1.5 10 tons of coal are present in these deposits (compare The Economy, Energy and the Environment, Joint Economic Committee of Congress of the United States, September 1, 1970). A processing of

^Y 18 only 30% of these coals would yield about 10,000 χ 10 cubic feet of gas, about thirty times the currently known minable reserves.

For the purpose of description, the present invention is based on " referred to a special coal deposit that is in the Central Powder River Basin-of east Wyoming approximately 20 miles west from Öillette. There are generally five separate layers of coal in this formation, each layer approximately 50 feet thick, although part of it has a continuous carbon fringe 200 feet thick. In an area of 9x18 square

1 row

miles there is enough coal to produce 700 χ 10 cubic feet of gas. However, this coal is too deep to carry out an economic extraction, so that the in-situ gasification would otherwise makes inaccessible reserves accessible.

A typical section of such a deposit is shown in Fig. 1, where coal layers 11 between shale-like Layers 12 are located, with a relatively close spacing. Above it then lies the upper layer 16, which is made up of scattered layers Layers of sandstone and slate consists, in which the groundwater layer 14 is at a certain level below the

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Earth's surface exists. In general, a formation is selected in such a way that that the uppermost coal layer is at such a depth below the water level that a hydrostatic pressure in the range of about 500 to about 10,000 psi or slightly higher. The hydrostatic pressure is approximate 435 psi for every 1000 feet below water. Furthermore, the formation should be chosen so that it averages contains at least about 20% carbon in order to obtain a satisfactory rate of reaction. The formation to be exploited can be a continuous layer, or coal with. Mixed rock.

The coal layers are used to process the selected coal store with the slate layers strewn in it - if any - shaken by explosives. The area covered is selected in such a way that enough coal is processed to ensure continuous operation for a considerable period of time, i.e. 1 year or more. Preferably, the coal is exposed to the vibration in as large an amount as possible that can be processed at the same time, so as to reduce the amount between areas to be processed to minimize remaining coal. One Half a square mile or more can be processed at one time. There can be explosives such as ammonium nitrate-aluminum-diesel or fuel oil mixtures or an ammonium nitrate fuel oil mixture (ANFO-Al or ANFO) are used, i.e. explosives, which are widely used in the mining and construction industries but it can also be used for plowshare applications. developed nuclear explosive substances are used. For example, can the usual explosives are introduced through 24 inch drill holes 17 (see FIG. 1), for example with spaced 60 feet apart in a concentric hexagonal pattern as shown in Figure 2 of the drawings. The boreholes used for the introduction of the reactants can be lined with steel pipes and sealed before the explosion with drilled stoppers or removable packaging to contain the detonation. In deny remaining The lining can be used for boreholes to - if necessary - prevent the entry of water.

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dern, or else it can just be filled in with waterproof

Material. The explosive means can be brought into place one after the other and detonated, for example starting from the central opening, in order in this way to a possible To prevent breakage of the overlying layer. The size of the explosive charge is selected to be adequate Fractional amount results, but no "lifting" detonation should occur, which could cause the formation to explode unnecessarily. Usual charging and ignition systems can be used. Per tonne of explosives one can break in the order of 600 tons Reach coal. It is also possible to use a smaller number of core devices, with the spacing and device size can be found in published information (see UCRL-50929, "Aids for Estimating Effects of Underground Nuclear Explosions ", T.R. Butkovich et al., September 8, 1970).

When the desired amount of coal has been broken, the detonation zone for carrying out the gasification process can be arranged in the manner shown schematically in FIG. The shaken or broken coal layer 21 can be viewed as being in a closed vessel or cavity, the vessel being defined by the surrounding undestroyed parts of the original formation. One or more of the cased wellbores 17 (only one shown) can be drilled to serve as a reactant inlet conduit. The line holes 17 can be connected to an oxygen supply system 22 and receive water through a water treatment system 23. A sufficient number of boreholes are used, or other means, such as spraying devices, are used to achieve a reasonably uniform distribution of the water on the top layer of the layer 21 of crushed coal. Oxygen is only distributed by injection or injection. At least one outlet line 24 (only one of these lines is shown) for the product is provided and is connected to the bottom of the broken coal layer 21 in order to release the gases (CH ₄ , CO, CO ₂ / H- * HO, etc.)

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to provide a surface gas cleaning system 26. The outlet conduit could also be constructed as a lined shaft with galleries or channels (not shown) / which lies underneath the broken coal layer and is lined. A centrally located shaft with several satellite gasification chambers could also be used. The gas cleaning system 26 can be designed in the usual way, as is the case with the gas cleaning systems used in above-ground operation. If the gas product mainly contains methane and CO - as is the case with certain operating modes - then the system 26 can manage with only one CO ₂ removal unit which, for example, _{absorbs CO 2} in water and a water condensation unit is provided, all the more so to generate gas suitable for pipeline transport. The excess water accumulating in the lower parts of the cavity can be withdrawn through a conduit 24 using a pump (not shown). When the hot zone of the gasification reaction approaches the lower parts of the coal layer, it can happen that the methanation is no longer complete and that CO and H _{2 appear} in the gas product. In this case, a catalytic methanation system of conventional design can be provided in the gas cleaning system.

The absorber water containing CO 2 can be circulated to the water treatment plant 23, where the CO _{2 is drawn out} in an extraction tower or by passing air bubbles through it. This water and the water drawn off from the cavity can then be used again in reaction with the coal layer. The initial water supply does not have to come from fresh drinking water, but stale water from a storage system can be used.

At the beginning of the process, a flammable mixture, for example oxygen and a fuel gas, for example natural gas, is led down and ignited in order to heat the uppermost layers of the coal layer to the reaction temperature, ie preferably to a range from about 65 ° K to about 11 ° ^P K; very loading

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the range from about 650 ° K to about is particularly preferred 850 K. Other ignition methods can also be used, such as. they are in use on oil feathers. During this process the product exit line 24 is closed so that the cavity pressure falls to the operating range - approximately 500 to 1000 psi or more - increases. Thereupon the product outlet line 24 is opened, whereby a gasification reaction zone with a Temperature profile of the type shown in Fig. 4 adjusts. The relative sets of. Water and oxygen generally become such regulated that the Spxtzenreaktxon temperature in the uppermost layers of coal remains at a level where water-gas reactions and some methane decomposition reactions occur. A more complete methanation then occurs in the cooler zone before the peak temperature zone. If the reaction proceeds over a period of time, the reaction zone will proceed according to ■ down, leaving ashes and rubbish behind. Passing through Water and oxygen absorb the residual heat from it in order to supply part of the heat required for the gasification reaction. .

It should be noted that the downward gasification process provides a very stable reaction front, which compared with an upward or side burning process that Minimized bypassing of unreacted charcoal. Furthermore, the reacted and not yet reacted parts of the eye and the coal ash are effective catalysts for the Carbon monoxide-water reaction and also powerful collectors for sulfur oxides, hydrogen sulfide and acid vapors, how they are created by using stale water can. The rock has a low thermal conductivity, so that no noticeable heat loss occurs. Also be Fly ash and heavy metal contamination in the long vertical column caught out of rock and ashes. So it is a synthetic natural gas produced, which does not pollute the environment Consequence.

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Chemistry of the coal gasification process

Charcoal is an organic compound, essentially none Contains free carbon in its natural state. she consists from a series of molecules; which three or four six-carbon rings with a phenanthrene-like structure own. The phenanthrene-like structure is partially saturated with hydrogen, so that "boat-like" shapes result. nitrogen and sulfur (not pyrite) are contained in the rings, while oxygen occurs mainly in the hydroxy form. These elements thus cross-link the basic ring structure into phenol-formaldehyde-like ones Polymers. Because of the hoop tension, the whole structure is so loose that water molecules leave the space between fill in loosely arranged parallel rings and form hydrogen bonds with the unsaturated carbon atoms, whereby the entire structure is given additional stability. This water makes up 10 to 30% of the weight of the in place and Issue, existing coal and is chemically part of the coal.

Coals are classified in a complicated way, and that is dependent on their oxygen / carbon ratio, the coking properties, the ash content, the behavior when heated and the sulfur content. For the present purposes it is sufficient to consider four major categories: anthracite coals, bitumen, Sub-bitumen and lignite. These are classifications in this order by generally increasing hydrogen / carbon ratios and generally decreasing heats of combustion and generally increasing oxygen content. The gasification process described here appears to be simpler with the coals of the sub-bituminous and lignite classifications applicable where the hydrogen / carbon ratios approach newly mined coal. This kind of coal has a large amount of built-in hydrocarbon and has a more favorable heat equilibrium in the case of gasification taking place in situ.

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Since every coal has a slightly different chemical structure a universally applicable set of reactions cannot easily be given. For the present purpose it is considered the gasification of the coal of the Central Powder River Basin as an example of widely distributed coal deposits. These Coal has a calorific value of approximately 9,000 BTU / lb and the chemical properties shown in Table 1. There is generally five layers of coal in the area, each La ge has an average thickness of 50 feet, although one borehole (Lake 29 T49NR75W) is 205 feet of continuous Yielded coal in one location.

T a b e 1 1 e 1

Analysis of the Powder River Coal ■

Natural occurrence analysis result

Moist volatile coal ash S H C NO ke.it parts fabric

21.4 33.7 38.6 6.4 0.8 5.6 58.6 1.0 27.5

The "formula" for the coal given in Table 1 is CH ₁ ^ g ^ O 35 ^N o 015 ^ o ΟΩ5 '^ ^ese formula for the thermodynamic calculations can be simplified to: CH ₁ i _C 0_ · ,, -. This coal

! • IQ UaJJ

has a formal weight of 18.76 grams; this weight should not to be confused with the molecular weight, which is probably closer to one or two thousand. In the following calculation the "mole" is used which is believed to be the simple one depicted above.

To calculate the thermal equilibria and the chemical reactions, it is necessary _{to know the enthalpy H 2} go and the entropy S ° 2ηο of the carbon compound. The enthalpy or the heat of the formation of the coal can be derived from the heat of combustion and the known heat of formation of the reactant oxygen

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and the combustion products are determined. This calculation shows that H ° ₂ 98 of ^this coal -30,627 Kcal mol "

is. '■,.

Estimating the entropy of the formation is more difficult and can be based on assumptions about the chemical structure of coal be performed. By comparing a number of organic compounds whose compositions are similar, the eritro-

* -1 -1

pie of coal can be estimated to be between 5 and 15 cal deg mol. Using the Lätimer rule to estimate the entropy, S ° _2g8 = ^ L (3/2 R / ηΜ _± -0.94), gives a value of 10.24 cal deg mol for the coal in question. This very important property can be determined more precisely by conventional test methods. There can be a shift in the optimal operating temperatures if the true value deviates significantly from the assumed value; however, an assumed value can be used to evaluate the heat and equilibrium reactions that occur. This choice does not significantly affect the thermal balance. A value of 10.1 cal deg mol is assumed for the following calculations.

The reactions occurring in coal gasification can now be investigated, with reference to -Fig. 2, attention is drawn to the four categories, ie combustion, pyrolysis, reaction with water and · with hydrogen. These are the compounds that come into contact with the carbon at the various locations in the active reaction zone. Neither CO ₀ nor CO react with coal at lower temperatures and these reactions are not included in Table 2.

The estimated Δη for the reaction and the free energy bJ? are shown in Table 2 for a temperature of 500 ° K and 1000 K ^0. According to conventional convention, a negative value of £ -H means that heat is released, while a positive value of AH means / that heat is consumed. Negative values of AF indicate reactions that favor the product or the right-hand side of the chemical equation, while positive values

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te profile of AF that the Reaktionsrnittel or standing on the left side connections are favored. "Accordingly, is carried out completely a reaction with a positive and a negative AH ^A F under heat consumption.

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σ ■ cn cn VO CM ο ¹ cn CVJ CO • • * t ^ O

in

σ ο

0 -H 4Y Ai (0 Q) pi

CTv

cn in H

ve

H CO

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VO t—

. = r cm ΐ = 3- cn

σ in co vo

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ΌΛ ι — I t ·· - CTV

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cm cn

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232700a

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The thermodynamic parameters in Table 2 show that the coal only decomposes or reacts with water (reactions 1 and 2) if heat is supplied at temperatures above 500 K.

ih

themselves

will. Therefore, with this coal and in the absence of oxygen or hydrogen (reactions 3 and 4), the reaction will not continue so that out-of-control of the combustion cannot occur. The reaction, which produces methane (reaction 2) directly from coal, requires the supply of heat and seems to be somewhat less favored at these temperatures than pyrolysis (reaction 1), so that the direct conversion of coal into methane with water is possible, if enough O _{2 is} drawn, leads to generate the required heat via reaction 4. On the other hand, the reaction 1 is faster than methane r is generated by the reaction of 1 and the

Carbon then reacts with water (reaction 5), some of the CO will further react with water (reaction 8) to produce enough hydrogen to equilibrate reaction 9 with the same net result. Two competing reactions can also be considered. This second way of methane production, ie from carbon, can be stopped if reaction 3 consumes all of the hydrogen / (although methane is in any case produced by other reactions), or if reaction 10 occurs and consumes all CO before reactions 8 and 9 can occur. Experiments with methanation devices used on the earth's surface show that the rates of reactions 8 and 9 are favorable under some conditions, while reaction 10 is favored among other conditions. However, if reaction 10 occurs, then when the higher temperature zone reaches the product carbon, reaction 7 will begin the entire cycle until the gas product is H2 and CO. This can be combined on the surface to form methane in the usual way using a suitable catalyst. The secondary reactions in Table 2 between C, CH ₄ , CO ", H" and H ₃ O are taken from a similar table in the following literature reference: "The Chemistry of Coal Utilization", Supplementary Volume 1968, J. Wylie Press, Chapter 21; Editor Homer Lowery.

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Various other conclusions can be drawn from this table to be pulled. Even at low temperatures, no oxygen can remain, since the reactions 4, 5 and all are exothermic with strongly negative free energies. Reactions 1, 2 and 7 consume energy at high temperature, while reactions 6 and 9 or 10 generate energy at low temperatures. This combination causes the Heat spreads through the reaction zone and ensures or helps that the combustion zone also crosses shale zones jumps without the need for external attempts at ignition when the reaction zone progresses downwards.

All the information in Tables 1 and 2 can be combined to determine an overall energy balance if the initial reaction temperature is selected. In the illustrative example below, it is suggested that water and oxygen just be added in such an amount that reaction 2 of Table 2 is maintained at 700 ° K. the The ambient temperature is assumed to be 300 ° K and the coal composition corresponds to the values given in Table 1. Under these conditions the heat required is that which is needed to keep the coal, ash and water from ambient temperature to bring to the reaction temperature and the Evaporate water and keep the reaction going. The heat supplied must be generated by burning the coal. For this calculation, it is useful to specify the thermodynamic quantities on a unit weight basis, as shown in Table 3 is shown. Although the above calculation is only approximate, as different heat capacities have been estimated, can they are used in the initial construction of the facility. Optimized conditions can be used with greater accuracy can be determined by computer simulation and / or by changing the operating conditions. The calculation leaves the products to 700 ° K, but a considerable part of this heat again Can be recovered when the hot gases pass through the cooler ones unreacted coal flows below the reaction zone and also during the flow of the input oxygen and water through the ash and spent material reaching the reaction zone and causing after the operation once in

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Gear is set, smaller amounts of O "are required. The water consumption was calculated as if all the water remained in the coal. It is most likely that Evaporate some water in the hot downstream gases and appears as a liquid condensate at the base of the crushed or fractured zone. In this case it will it is pumped to the surface and, if necessary, injected again.

T ^r a "belle 3

1.1g charcoal in place = 0.936 charcoal + 0.064g ash

2.1 g charcoal + 1.9, gO ₂ - * - 2.34 g CO ₃ + 0.56 g H ₃ O (g)

ΛΗ = -5291 cal / g coal

3. 1 g charcoal + 0.513 g H ₃ O (g) - * ► 0.475 g CH ₄ + 1.038 g CO ₃

ΛΗ = 529 cal / g coal

4. 1 g coal about 300 ° K - * · 1 g coal approximately .700 ⁰ K

ΔΗ = + 255 / cal / g.

5. 1 g H ₂ O (1) - * 1 g H ₂ O (g) (T = 393 ° K)

Δ H = + 575 cal / g

It is X. equal to the coal located at the point, which for Generation of heat is to be burned, assuming that one gram of the coal in the place is converted into methane is converted. The equation for thermal equilibrium is the following:

0.936 κ 5291X -255X = 255 + 529 χ Ο.936 + 0.936 χ 575 / Ό. 51 3 -0. 936 * 0.

X. = 0.206

Thus, essentially 0.2 grams of the coal in place for each gram of the water converted on-site coal to be burned. Table 4 summarizes the products and reactants per ton

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the coal on site.

Table 4

Reactants '

Coal in place Oxygen "'

water

1 metric ton 0.304 tons

0.306 tons 306 1

Products

methane

Carbon dioxide

ash

nitrogen

0.370 tons 19.8MCF

1.175 tons 22.9 MCF 0.064 tons

0.0072 tons of 0.22 MCF

0.0058 tons 0

It cannot be predicted whether sulfur will appear as SO- or HS, but CS- is not detected at low temperatures. Either SO ₂ or H ₂ S will likely react with the shale and be absorbed before it gets into the product pipeline, producing a gas with a low level of pollutants.

The calorific value of the coal used is 9000 BTU per Ib (pounds sterling) or 19.8 million BTU per metric ton. The calorific value of the methane produced is 18.6 million BTU, so the calorific value of the coal is largely preserved with this process remains, although only 46.4% of the coal is converted into methane.

The small loss is the heat left in the hot ash, shale, and gas. The shale layers between the coal layers will require some heat, but assuming _R that all of the product heat is provided by the coal and that the products or products are left at the reaction temperature, this loss does not reduce the reaction efficiency. It is indeed the case that Table 4 is based

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lying thermal equilibrium as extremely pessimistic from the efficiency standpoint must be considered and that in practice an even more favorable result will be achieved,

Procedure:

If one starts with the comminuted coal system of FIG. 2 and accepts methane as the product, then the one described above can be used thermodynamic theory to select the best operating conditions of the coal gasification process. The procedure to be described is thus for comparison with others Gasification process and useful for approximate profitability analyzes.

The schematic system arrangement shown in Fig. 3 can be used. The oxygen system can be a standard cryogen unit which has a high pressure injection pump. The water treatment system can simply consist of a storage tank, a CO ₀ extraction unit (if the water is to be reused) and a pumping system including a high pressure injection pump. The gas cleaning system can be of conventional design and is capable of removing SO- if any in the end product. However, it is highly likely that the SO _{9 will form} in the earth and in this case it will be absorbed by the shale by reaction with carbonates so that no sulfur oxide gases are present in the finished gas. This is a very important and environmentally very beneficial consequence of the in-situ process in contrast to coal gasification carried out on the earth's surface. The CO ₂ can be removed by washing with water or by expansion cooling. A simple high-pressure potassium carbonate wash could also be used for the CO ₂ removal, in which case any sulfur compounds present could then also be removed at the same time. The solution could then be recycled and used again.

The size of the plant or factory depends on the z; u generating Gas volume and thus in turn from the vicinity of the pipeline. If both

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for example the desired rate is 100 BCF per year and if so one assumes that every broken, dreary, crushed unit of coal of the type shown in Figure 3 is processed in a year and over 5 million metric tons of coal in place the overall requirements are given in Table 5.

Amount of gas generated. Coal consumed

Oxygen consumed

Used water

Drill holes.

Table 5.

Yearly.

Daily

100 BCF

274 MMCF

5.05 million 13 * 8 thousand metric metric tons tons

1.53 million 4.19 thousand metric metric tons tons

1.54 billion 4.23 million liters liters

0.6

(For example, 24 inches by 60 feet) Approximately 9 kilotons (ANFO-Al) of explosives

This method requires that the coal be burned from top to bottom only in the zone broken up by the explosive. This ensures maximum stability at the combustion front and avoids one of the main problems with known in-situ gasification attempts where the input gases could flow past the coal. Units to be processed consecutively should be far enough away so that no gas flow past can occur in a previously burned-out zone. However, after the earth has settled, it is possible to process the remaining coal later. This Makes it convenient to process large area simultaneously, as is indicated in Fig. 2. The zone indicated in the lower part of FIG. 2 corresponds in its scale to approximately 100 BCF per year of operation.

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It also appears that the in-situ process takes place under very favorable kinetic conditions. Fig. 4 shows a presented vertical section through the carbon zone in reaction together with the chemical reactions and the approximate temperature distribution. The inlet zone water is evaporated and heated. As soon as the gases reach the coal, oxygen and water react very quickly and create the high temperature peak; in the downstream zone, carbon monoxide and water react at low temperature to produce carbon dioxide, methane and heat. This heat creates the ^N extended intermediate temperature zone. Eventually, at the lowest temperature, water evaporation and condensation occur. The thickness of the very high temperature zone is unlikely to exceed 10 meters in length.

Taking gas generation rates from Table 5 and the area or zone from Figure 2, it is found that the superficial gas velocity in the crushed coal is 0.1 feet / minute, and with a reasonable average porosity of the crushed coal should the actual gas velocity will be 15 to 20 cm min. The Reafctioriszone should be about 10 m thick, so that the available The reaction time in the high-temperature zone is thus on the order of 1 hour.

Data from experiments in the 1100-1300K range indicate that the reaction kinetics belongs to the pseudo-first-order and one Average temperature dependence follows. Based on the observed rates at the higher temperatures, the Rates for complete reaction at 700 ° K are estimated to be on the order of 1 hour, which is comparable to residence time. Accordingly, the maximum operating temperatures in the present Procedures are reduced compared to conventional ones Process where high reaction rates are required for economic operation required are.

An economic analysis indicates that the cost of capital requirements between 15% and 30% of surface factories of similar capacity. The running costs are good with

comparable to those of the surface systems, so that

The profitable selling prices of the produce are considerable can be smaller (between 27-92% less) than for gas from a surface facility. Because this cost is not are too dependent on interest rates, there is a considerably lower overall risk for the investor or for the evaluation investment costs incurred in the process.

The drilling costs constitute and have been the main operating costs Estimated assuming the drilling rigs (9) were purchased and by permanent operations crews throughout the year to be used. This results in significantly lower "per foot" drilling costs. In this analysis, the Use of ammonium nitrate explosives assumed. the

too same amount of coal could be caused by about 9- / kt nuclear explosions to be broken. In this case the explosives would be more expensive and the drilling costs would be lower.

On balance and in view of the accuracy of this analysis, the total cost could be up to 6 US c per MCF less when using nuclear explosives, depending on the size of the seismic damage. Only about 9 kt of chemical explosives are required, and they are introduced in such a way that the ground is not raised. Should the underground methanation not be complete, the construction and operation of a surface methanation facility to complete this function would increase the price of gas by approximately USc 18 per MCF (MCF = 1000 cubic feet; MMCF = 10 ⁶ cubic feet; DCF = 10 ¹² cubic feet).

309850/0462

Claims (8)

7327008 ίν CLAIMS 1. Process for in-situ gasification of an underground Coal deposit for the production of a synthetic natural gas characterized by the following process steps: Selection of a coal storage formation with a relatively thick coal layer 11, which is below the water layer is located at a depth which will provide a hydrostatic pressure of at least about 500 psi; Insertion and detonation of explosive charges 19 in the Coal-containing layer of the formation to form a deep layer of crushed coal in one through the - closed cavity 21 formed by undestroyed parts of the formation; Providing at least one reactant inlet line M _r which is in communication with the uppermost layers of the fractured coal layer in the cavity t together with at least one product outlet line 24 which is in communication with the lowermost parts of the coal layer in the cavity; Injecting oxygen through the inlet line and Ignition of the upper layer parts of the coal layer, the operating pressure in the cavity for equilibrium is raised with the hydrostatic pressure; then injecting water through the inlet line for a reaction with the ignited layer of coal, namely with "Sufficient oxygen to make the reaction necessary To provide heat while the reaction product gas is withdrawn through the product discharge line to a reaction zone, to form, which has an upper high-temperature layer zone, which gradually decreases in the lower zone with Temperatures penetrates, with the reaction zone downwards advancing through the coal layer so that a methane containing product Gas.an is delivered to the flue; Separation of the methane from the product gas delivered through the product discharge line. ■ '. '3Ü985Q / 046? 7327008 2. The method according to claim 1, characterized in that the layer containing the coal has a composite thickness of at least about 50 feet. 3. The method according to claim 1, characterized in that the high temperature zone in the reaction zone is in the range of about 60O ⁰ K to about 15QO ° K .. 4. The method according to claim Ί, characterized in that the temperature in the high temperature zone of the reaction zone ranges from about 65o ° K to about 1100 ° K. 5. The method according to claim 4, characterized in that the Product gas including a mixture Methane and CO «. 6. The method according to claim 4, characterized in that the product gas has a mixture including methane CO ~ / CO and H2, wherein the gas is further processed in a methanation device arranged on the surface in order to complete the methanation reaction, with the remainder being CO ₂ is removed from the product gas to produce a high quality synthetic natural gas. 7. The method according to claim 4, characterized in that the operating pressure in the cavity in the range of 500 to is about 1000 psi. 8. The method according to claim 7, characterized in that the temperature in the high temperature zone is of the order of magnitude of 700 ° K. 3 0 9 8 50 / G46? Blank