GB2035366A

GB2035366A - Treating brown coal or lignite

Info

Publication number: GB2035366A
Application number: GB7934642A
Authority: GB
Original assignee: Gaskombinat Schwarze Pumpe VEB
Current assignee: Gaskombinat Schwarze Pumpe VEB
Priority date: 1978-10-16
Filing date: 1979-10-05
Publication date: 1980-06-18
Also published as: IN152361B; JPS5589393A; AU5163079A; ATA557779A; HU182961B; PL127068B1; YU250179A; DE2935594A1; DD145180A3; NL7906674A; PL218799A1; JPS5839471B2; SU1041559A1; GB2035366B

Abstract

Granular crude brown coal or lignite is introduced into a pressure steaming chamber at a pressure above 1 MPa, where it is partially dehydrated by means of an evaporation agent, e.g. steam, pressure carbonized, uniformly shrunk and heated substantially uniformly to a temperature above 423 DEG K it is then conveyed without expansion to a pressure of less than 0.5 MPa into a pressure degasification and pressure gasification chamber, in which it will undergo further non-destructive drying as a result of its heat content, the pressure degasification and pressure gasification of the treated brown coal or lignite being subsequently effected.

Description

SPECIFICATION A process for the pressure degasification and pressure gasification of crude brown coal or lignite The invention relates to a process for pressure degasification and pressure gasification of crude brown coal or lignite, especially of soft brown coal or lignite, in which the drying of the brown coal or lignite is directly connected with the pressure degasification and pressure gasification process and the energy required for the drying process is reduced to a minimum. The drying is effected in an extremely non-destructive manner, so that the direct use of granular crude brown coal or lignite with a high water content, especially soft brown coal or lignite, can take place without the grain disintegration which detracts from the degasification and gasification process.

The use of the process to which the invention relates enables granular crude brown coal or lignite with only a slight degree of carbonization to be gasified under pressure in a solid bed or in a fluidized bed and it is possible for even a granular smokeless fuel to be produced.

Systems are known in which brown coal lignite, especially soft brown coal or lignite, are used for pressure gasification in a solid bed orfluidized bed.

If the coal or lignite is used in briquette form in solid bed pressure gasification the systems so far known involve expensive preparations of the brown coal or lignite, including the operation of working up the fine grain, the drying and the pressing. With high specific outputs of the pressure gasification process the briquette is not found capable of standing up to the high thermal stresses and disintegrates in the after-drying and degasification taking place in the gasification reactor, in addition to which considerable quantities of dust are emitted by crude gas of the pressure gasification. Furthermore, grains from soft brown coal or lignite have been used in the pressure gasification process which had been dried in tubular dryers outside the gasification plant.

The pressure gasification process with high specific outputs and also without any increase of dust was hitherto only possible with the use of dry grains of hard brown coal or lignite and with the use of pit coal. In the case of grains of soft brown coal or lignite dried in tubular driers, on the other hand, acceptable dust emission with the crude gas could only be ensured with very limited specific gasification performances. To increase this latter, soft brown coal or lignite is at present mainly used in the form of briquettes in solid bed pressure gasification. In the briquetting and drying plant a considerable amount of technical equipment, attendance and maintenance are required. The dust causes serious pollution of the environment.

Owing to the dry coal dust which forms there is always a serious danger of explosion in the plant.

Considerable wear occurs in the transport of dry fuels. Furthermore, the energy required when the drying is effected bytheevaporation method is considerable, as are also the resulting waste heat losses.

A number of suggestions have been put forward in the past for the purpose of eliminating or reducing the disadvantage involved in the use of soft brown coal or lignite. Ger.Dem.Rep.Pat. Specification 26392, for instance, suggests that the material to be gasified should be irrigated with gas water, before reaching the pressure gasifier and/or in the latter, intensively enough to lower the temperature at which the gas emerges from the fuel bed.

Ger.Dem.Rep.Pat. Specification 38701 describes a process in which only part of the hot gasification material is used for the degasification and drying of the fuel, the residual gas being withdrawn separately.

Similar proposals to those described in the foregoing are also to be found in Ger.Dem.Rep.Pat.

Specification 119814.

Ger.Dem.Rep.Pat. Specification C 10 J/205 413 proposes that the quantity of crude gas for afterdrying and degasification should be regulated in such a way that a certain preselected heating speed will occur in certain temperature ranges and the preliminary drying is carried out in a manner that largely leaves the properties of the material unimpaired.

Ger.Dem.Rep.Pat.Specifications 121796 and 120043 recommend an increase of the fuel used to 20-24% in the case of briquettes and to 45% in the case of dry lump coal.

The suggestions indicated have hitherto not found a footing in practice. It is true that they would enable the disintegration of the fuel in the pressure gasification reactor to be kept within certain limits, but they also entail additional drawbacks and extra requirements from a process engineering point of view.

These known suggestions are based on the use of briquettes or on convection-dried grains of coal, with the drawback from which they suffer, i.e. their inadequate stability in pressure degasification. They also do not alter the fact that the production of briquettes and dry grains necessitates considerable outlay on plant, energy and attendance. For example, the evaporation of water from coal alone calls for a quantity of heat, in relation to the water evaporated, amounting to 3100-3300 kJ/kg.

Hard brown coal or lignite cannot be easily briquetted. Based on this realization a process was introduced aslong as 50 years ago for drying the hard brown coal or lignite and largely preserving its lumpy property. This was described for the first time in Ger. Reich Pat. Specification 466617 and became known as the FLEISSNER process, after its inventor, or as the pressure steaming process. It consists of the heating of coal, under pressure, with saturated steam, the water being then unable to evaporate.

Owing to the shrinkage occurring in the heating of the coal, and the CO2 separated, some of the water is expelled in liquid form. This reduces the energy required for the separation of the water and also ensures a largely even heating and shrinkage of the grain, as the water separated does not continuously remove the transmitted heat from the grains of coal, as it does in the vaporization drying process.

In addition to the original process described a number of suggestions were made for the planning and further development of this method. The improvement of the thermal economy, for example, was the main aim of the processes described in Ger.

Reich Pat. Specification 520369, in which hot water in place of steam was used as the steaming agent, Ger. Reich Pat. Specification 527021, using superheated steam, Ger. Reich Pat. Specification 583907, Ger. Pat. Specifications 1049312 and 1189465, Austrian Pat. Specifications 185349, 190490 and 244292, etc. The invention forming the basis of Ger.

Pat. Specifications 1201254 and 1243109 represent an attempt to make the process continuous. These methods, however, involve considerable process engineering outlay, so that no continuous process has so far found a footing in practice.

The advantage of the process consisting of the pressure evaporation of coal resides in the very moderate energy requirement, i.e. 1400-1700 kJ per kg of water separated, and in the fact that the coal is dried without detracting from its properties. This method of drying, by comparison with the conventional method, suffers from the drawback of necessitating more highly stressed steam. In the expansion of pressure-steamed coal some of the water is evaporated at low pressures and in a pressureless state. This process necessarily results in a narrower water-content range and in damage to the grains of coal, even if to a far smaller extent than in convection drying. After the expansion a limited reabsorption of water by the coal is possible.The pressure steaming process has hitherto been introduced in the case of the use of hard brown coal or highly lignitic brown coal. There have also been cases in which highly lignitic brown coal has been conveyed to a pressure degasification plant and gasified in a solid bed, having previously been dried with steam in a pressure steaming plant.

In the pressure evaporation of dusty briquet table soft brown coal or lignite there is a risk of a high sludge content. Attempts have been made to evaporate soft brown coal or lignite of this kind, but solely for the purpose of using the dried coal or lignite for briquetting or as fuel in furnace systems. It has been found that dehydration of the coal or lignite to below 30% by weight can only be effected at considerable expense and that the pressure evaporation of coal or lignite usually detracts from its briquettability. The increased water content following the drying renders transport uneconomical by comparison with briquettes. For the rational utilization of water heat the pressure evaporation process necessitates a number of interconnected pressure vessels and numerous connecting pipes. The dehydrated coal or lignite has to be cooled after the steaming.The outlay involved on machinery is increased still further owing to the non-continuous operation of this method. The latter thus involves expensive equipment and labour. The resulting dust causes pollution of the environment and leads to a risk of coal dust explosions.

The purpose of the invention is therefore to combine the drawing of the crude brown coal or lignite directly with the pressure degasification and pressure gasification process and thus to enable the coal or lignite, particularly in the case of soft brown coal or lignite, to be dried in a manner leaving its properties largely unimpaired.

A further object of the invention is to reduce the thermal energy requirement, the outlay involved on plant and the cost of its operation.

In the pressure gasification of brown coal or lignite, particularly in the case of soft brown coal or lignite, the considerable quantity of dust occurring in the crude gas undergoing the pressure gasification has been found, as already described, to constitute a particular disadvantage.

More recent investigations suggest the following reasons for the disintegration of the briquette: The briquette structure is largely held together by cohesion forces set up by the water contained in the dry coal. After the evaporation of the water the residual binding forces only result in a very loose and abrasion-prone briquette structure. Gasification briquettes, which are pressed, as is well known, from coarse-grained dry coal, are particularly liable to disintegrate under a high thermal loading. The briquettes are also at a temperature of about 303-313 K when placed in the gasification reactor, in which temperatures of 623-774" K prevail. This thermal shock causes the briquettes to heat up unevenly.The outermost briquette layers dry more quickly, thus undergoing more shrinkage, and stresses are caused which accelerate the disintegration.

The grains of dry coal in the briquette structure also contain different proportions of water, which are greater, the higher the average proportion of water.

In the drying of the briquettes in the gasification reactor, therefore, these grains shrink considerably, which likewise causes noticeable shrinkage of the briquette structure. The disintegration of the dry grains of coal or lignite, particularly those of soft brown coal or lignite, is due to the following: the drying of the grains of soft brown coal or lignite takes place by convection drying, usually in tubular dryers, as a result of the evaporation of the water.

The evaporation commences on the outermost layers of the grain and only takes place inside the core after a considerable time lag. In the completely dried grain this leads to a difference, sometimes over 30%, between the water content of the "shell" and that of the core. Owing to the resulting considerable shrinkage of the outer shell by comparison with the core the latter loosens and becomes very sensitive to abrasion. The high volume of steam forming in the drying is prevented by the coal or lignite mass of the grain from emerging and forces a free path for itself by means of the expansion force, so that the grain structure is partly destroyed. These grains cool down to about 303-313 K on their way to the generator plant. The grains of coal or lignite dried by convection drying have to be cooled, in fact, in order to avoid spontaneous combustion of the coal. These coal or lignite grains are subjected in the generator to momentary temperatures of 623 -773" K. By the time the interior of the grains has reached the boiling point of the water, a considerable shrinkage process suddenly takes place, starting from the shell of the grain and proceeding towards the core, and leads to further destruction of the grains of coal which have already been weakened in the preceding drying plant.

The phenomena described above only occur slightly, if at all, in the pressure degasiification of pit coal and hard brown coal or lignite, owing to shrinkage (carbonization) already caused in these types of coal by their very nature and owing to the consequently low water content. It has not previously been realized that the direct connection of pressure steaming with pressure gasification, from the process engineering point of view, constitutes one of the most harmonious connections in the process engineering of coal refining, enabling the defects inherent in the known technical solutions, and described in the foregoing, to be largely surmounted.

According to the invention there is provided a process for pressure degasification and pressure gasification of crude brown coal or lignite, comprising introducing granular crude brown coal or lignite into a pressure steaming chamber at a pressure above 1 MPa, partially dehydrating the brown coal or lignite in the said chamber by means of an evaporation agent, pressure cabonizing, uniformly shrinking and heating it substantially uniformly to a temperature above 423"K and conveying the thus pre-treated brown coal or lignite without expansion to a pressure of less than 0.5 MPa into a pressure degasification and pressure gasification chamber, in which the coal or lignite will undergo further non-destructive drying as a result of its heat content, and subsequently effecting pressure degasification and pressure gasification of the treated brown coal or lignite.

In a preferred form of process embodying the invention granular crude brown coal or lignite intended for the pressure degasification and pressure gasification process, especially soft brown coal or lignite, with a water content of 55-60% by weight, is conveyed from a bunker or other receptacle in the known manner and, by means of a coal sluice, subjected to pressure and then caused to enter an evaporation chamber, in which the pressure prevailing will as far as possible be the same as in the degasification and gasification chamber, or over 1 MPa, but preferably over 2 MPa. In the evaporation chamber the crude brown coal or lignite is dehydrated and pressure-carbonized with an evaporation medium, preferably with saturated steam.The hot coal or lignite thus pre-dried is now caused to enter the degasification and gasification chamber, preferably without pressure expansion, but under no circumstances with expansion to a pressure of less than 1 Mpa, and preferably without cooling, but under no circumstances with cooling to a temperature of below 423"K. Owing to the high heat content of the coal or lignite pre-dehydrated by the pressure steaming, the said coal or lignite is further dried in the degasification and gasification chamber, in such a way as to preserve its properties, and then subjected to the degasification and gasification. It has been found that the pressure steaming of soft brown coal or lignite does not cause any great quantity of extra-fine grain to occur and that only some of the large grains disintegrate into medium grains.A disintegration phenomenon of this kind, however, hardly has any disadvantageous effect on the pressure degasification and pressure gasification process, particularly since the dehydrated grains show a comparatively high degree of resistance to abrasion. The water dripping off the coal in the pressure steaming frees it of the very fine grain and is in most cases separated continuously in the pressure evaporation chamber. This cleaning effect can be intensified if recycled hot evaporation water is sprayed through a nozzle in the steaming chamber above a pile of the coal or lignite. The continuous fuel requirement in the degasification and gasification chamber also enables the pre-dried coal or lignite to be continuously transferred to this latter.

The steam used for the pressure steaming is saturated at the pressure selected for the process and conveyed into the pressure steaming chamber above a pile of the coal or lignite in a quantity which ensures that a slight residual quantity of steam will always flow into the degasification and gasification chamber together with the gases occurring in the carbonization of the coal or lignite.

The steam can also be conveyed in a slightly super-heated state into the gasification chamber. It has been found that crude brown coal or lignite, especially soft brown coal or lignite, gives off the greater part of the water at the beginning of the evaporation and that it is not necessary to continue the pressure evaporation until the residual quantities of water have been given off at the pressure concerned. The coal or lignite thus predehydrated and heated stands up to the subsequent stresses of after-drying and heating in the degasification and gasification chamber without undergoing any major damage.The essential requirement is that the crude brown coal or lignite, in the pressure steaming, should be heated up uniformly to a temperature approximately the same as or higher than that occurring as the boiling temperature under the conditions of the process, but to at least 423" K, and that the shrinkage process should take place uniformly but should be largely terminated before the coal or lignite enters the degasification and gasification chamber. Even if the coal or lignite still has a higher water content, amounting to 35-40% by weight, for example, this is no great drawback. The resulting steam, in the after-drying in the degasification and gasification chamber, only has a slight fraction of the volume at atmospheric pressure and can flow through the mass of coal or lignite without loosening the structure of the latter.At a grain temperature between 423" K and the boiling point according to the pressure selected for the process, the transport of the water from the core to the shell of the grain, as a continuation of the steaming process, also takes place in largely liquid form. As the pre-dried coal or lignite enters the degasification and gasification chamber without cooling or coming into contact with air, the surface of the grain is not oxidized or hardened but remains plastic.

This does not impede the emergence of steam in the after-drying process. No reabsorption of water can occur. The heat carried along by the pressuresteamed hot coal or lignite into the degasification and gasification chamber is sufficient, for example, to dry the coal or lignite from a water content of 35-40% by weight to the 20% by weight otherwise usual when briquettes are used, i.e. without withdrawing further heat from the said chamber. These effects, which were hitherto not observed, cause the coal or lignite pre-treated by pressure steaming to be after-dried in the degasification and gasification chamber without impairing its properties. The complete dehydration of the coal or lignite in the pressure steaming enables the evaporation period to be shortened and the size of the steaming chamber to be thus reduced.

It has also been found that the grains of coal or lignite dehydrated under pressure only suffer slight disintegration in the pressure degasification, by comparison with briquette, and that the coke formed shows higher resistance to abrasion. As a result, however, the pressure-dehydrated grains of coal or lignite can be conveyed through the pressure degasificaton zone into the pressure gasification zone practically unimpaired.

The evaporation water occurring in the pressure steaming is expanded, and the steam occurring at atmospheric pressure and optionally the hot water likwise are utilized for preheating the crude coal or lignite to about 373O K. The evaporation water can also be used for the production of hot water. It is also possible for the expanded hot water to be used for the hydraulic transport of the crude coal or lignite to the bunker and for the evaporation water under pressure to be used for the transport of the crude brown coal or lignite from a coal sluice to an evaporation vessel preceding the degasification and gasification reactor. In the latter case a preevaporation is effected by the hot water.To enable the evaporation chamber to be kept small it is advisable for the crude brown coal or lignite to be prepared in advance in the coal sluice by means of a partial flow of the evaporation agent and/or by means of hot evaporation water.

In the pre-drying of the crude brown coal or lignite by a process embodying the invention the heat requirement when the evaporation water is used for heating the crude coal or lignite to 363 K only amounts to 1000-1200 jKfor each kg of water separated in the pressure steaming and is thus lower than in the case of separate pressure steaming plant.

The advantage of this system resides in the fact that the hot coal or lignite, after the evaporation, causes no additional waste heat losses and that this heat from the coal or lignite is fully utilized in the degasification and gasification process and in the subsequent waste heat utilization process. As the evaporation process can be carried out continuously, the heat losses which would be caused by the cooling of the evaporation vessel and the intermittent heat expansion are obviated or minimised.

The supplementary outlay on apparatus is very moderate, since the process is integrated with the pressure degasification and pressure gasification.

The method to which the invention relates makes it possible for the pressure steaming and also the degasification and gasification to be combined in a pressure vessel of appropriate size. Owing to the integration of the system in the degasification and gasification process the feed, evacuation, CO2 removal and coal-cooling devices otherwise required in pressure steaming plant are no longer required.

Any supplementary steam supply to the degasification and gasification plantforthe pressure evaporation is usually unnecessary, as the gasification steam supply can be utilized. The vessels for the pressure degasification and pressure gasification usually have a water jacket to protect the outer casing subjected to the pressure. The steam generated in this water jacket can be used with great advantage, in the process described, for the purpose of pressure steaming.

The process to which the invention relates necessitates no additional personnel.

The heavy expenditure already described and hitherto usual for separate production of dry coal or lignite can be eliminated. As no coal or lignite dust can emerge into the open, the process does not pollute the environment. No coal dust explosion can occur.

The misgivings concerning increased sludge resulting from the pressure steaming of soft brown coal or lignite are unjustified. If we compare the method with the use of briquettes in pressure degasification and gasification, we find that 3% losses occur in the briquetting and 10-15% as a result of dust produced in the pressure gasification, these losses mainly occurring in the form of sludge.

The proportion of sludge in the process illustrative of the invention is largely dependent on the way in which the individual steps in the process are effected but does not exceed that occurring with the use of briquettes.

The process according to the invention also enables use to be made of coal or lignite with a high ash content, which could otherwise not be used, if a briquetting stage were interposed, owing to the serious wear then occurring. In the pressure steaming process some of the ash, particularly the very finely dispersed particles, is separated together with the evaporation water.

By comparison with the use of briquettes at present customary for pressure degasification and pressure gasification the crude brown coal or lignite treated by the process to which the invention relates is rendered more "shingly". This improves the mobility of the loose material in the generator and prevents the formation of bridges and channels which, in the gasification process, cause more dust and render the operation of the generator less economical.

The combination of the pressure steaming process with the pressure degasification and pressure gasificaton can also be carried out by effecting coal sluicing and pressure steaming in a vessel, an enlarged coal sluice, as itwere. In this case the pressure steaming process is carried out intermittently, just like the coal sluicing. According to this embodiment of the invention a number of vessels for coal sluicing and pressure steaming may then be associated with the degasification and gasification reactor and supply hot pre-dehydrated coal or lignite to the said reactors in alternation.

In this variant drawback as to the non-continuity and the increased thermal energy requirement is baianced out by the fact that no steps need to be taken to ensure a uniform movement of the loose material in the evaporation chamber, that no problems arise in separating the evaporation water and that the pressure steaming can be carried out with a higher and possibly with a lower pressure than that prevailing in the pressure degasification and pressure gasification chamber.

If it is desired to use a very dry fuel for the pressure degasification and pressure gasification process the pressure steaming with saturated steam can be followed by after-drying with superheated steam. To accelerate the dehydration process the evaporation in this variant likewise can be carried out with a greater quantity of residual steam. This leads to a higher flow velocity of the steam in a pile of the coal or lignite and thus to more satisfactory heat transference to the coal or lignite.Just like the steam discharged, the quantity of residual steam with the derived CO2 is used as the gasification agent in an after-drying operation carried out with superheated steam after the pressure steaming. Afurtherfact which has hitherto not been realised is that the hot crude gas leaving the pressure degasification and pressure gasification process and containing a considerable proportion of steam can be used with great advantage as a pressure steaming agent. The crude gas of the solid bed pressure gasification is characterized, on emerging from the reactor after saturation, by a very high partial steam pressure which, when soft brown coal or lignite is used, and is several times that of the partial pressure of the gas.The crude gas therefore still has the high temperature required for the steaming process, even after saturation with steam and after it has been freed of dust and condensed particles of carbon.

The use of crude gas from the pressure degasification and pressure gasification process enables the combined pressure steaming and pressure degasification and pressure degasification and pressure gasification process to be simplified still further. The crude brown coal or lignite, particularly soft brown coal or lignite, may be placed in a pressure vessel in which the pressure steaming and also the degasificaton and gasification process are effected. The crude gas generated in the bottom of the vessel by the partial combustion of the coal or lignite in the solid bed flows upwards in the opposite direction to the coal or lignite, carries out the gasification, after-drying and pressure steaming in the various zones that build up and then emerges from the top of the pressure vessel.The water leaving the crude brown coal or lignite in drops in the course of the pressure steaming saturates the crude gas ascending from the after-drying zone. The quantity of water given off by the crude brown coal or lignite, particularly when soft brown coal or lignite is used, is nevertheless generally far greater than the quantity of water required for the saturation of the crude gas. According to the parameters which may be selected for the process, some of this surplus water is conveyed out of the pressure vessel in the form of spray, together with the crude gas. According to the parameters which may be selected for the process, some of this surplus water is conveyed out of the pressure vessel in the form of spray, together with the crude gas. The remainder enters the after-drying and degasification zone, where it is evaporated, with the extraction of heat.This latter process increases the quantity of gasification agent and fuel required.

This can be prevented if devices for the separation of water are installed between the pressure steaming zone and the after-drying zone. These devices at the same time enable recycled evaporation water to be sprayed in the upper part of the pressure vessel, the material thereby being freed, to a still greater extent, of the fine dust occurring in the steaming process and also that carried along by the crude gas.

The hydrocarbons which have condensed out in the cooling of the crude gas during the steaming process improve the mobility of the loose materials in the evaporation chamber, thus opposing the very disadvantageous formation of bridges or channels, even in the subsequent zones. Of the steam contained in the crude gas only a small proportion is condensed out in the pressure steaming, so that the crude gas only undergoes very little cooling.

It is thus possible and also appropriate for the crude gas, after it has left the reaction vessel, to be utilized, in a manner known, for the production of waste heat steam.

The heat required for the preliminary drying of the crude brown coal or lignite in the pressure steaming zone is limited, when the heat of the evaporation water is used for pre-heating the crude coal or lignite to 3630 K, to 550-650 KJ per kg of water separated in the steaming process, this quantity of heat being taken from the production of waste heat steam by the crude gas. The use of high-pressure steam can thus be dispensed with. It is this realisation that indicates the great value of the suggestion for the use of crude gas for pressure steaming.The comparatively very limited thermal requirement for the drying of the coal or lignite is due to the fact that the process of pressure degasificaton and pressure gasification combined with pressure steaming suffers no additional heat losses from the hot coal or lignite or from the hot condensate occurring in the pressure steaming.

A further characteristic of the principle of the invention is the intensive flow of the mixture of steam and the gaseous constituents of the crude gas through a pile of the coal or lignite to be pressuresteamed, thus accelerating the heating of the coal or lignite, the chemical process of carbonization and the removal of gaseous constituents which form and thus the entire process of lyopolar and capillary liberation of water. These advantages are also obtained in the use of hot crude gases containing steam, particularly those free of phenol, which are produced in other pressure processes with the partial oxidation of fuels, and also take effect to a considerable extent when the dehydrated coal or lignite, expanded after the pressure steaming, is put to further use.

As only a small part of the steam contained in the crude gas is required for the pressure steaming process, it is possible for the latter to be carried out simply with partial flows of the crude gas produced in the combined gasification process. In this case the partial steam pressure in the crude gas in the pressure steaming must not fall below 0.5 MPa.

The principle of effecting the degasification and after-drying of the fuel with only part of the flow of crude gas produced is known in itself. This leads to the formation of a so-called low-temperature carbonization gas, and the rest of the gas produced in the gasification is extracted in the form of a so-called clear gas, free of tar. When soft brown coal or lignite is employed this low-temperature carbonization gas is comparatively free of dust, while greater quantities of the latter accompany the clear gas. The subdivision of the crude gas produced into these two separate flows also enables an adjustable heating speed, such as known per se, to be adopted in the after-drying and degasification zone, this being of advantage for the further treatment of the fuel in such a way as to leave its properties unimpaired, particularly in the degasification zone.

The low-temperature carbonization gas, owing to its low dust content, can be advantageously used for pressure steaming, in which case, after flowing through the degasification and after-drying zone, and immediately after saturation, it is conveyed into the evaporation chamber and generally flows from the bottom upwards through a pile of the coal or lignite.

If only the clear gas is used for the pressure steaming, this provides the advantage that this clear gas can be extracted from the reduction zone at such a high temperature that it is free of phenol, the dephenolization plant thus not suffering from the evaporation water forming. In this system the extracted clear gas is not to be conveyed into the evaporation chamber, above the pile of coal or lignite, until it has been freed of dust and saturated with water. With the use of one common pressure vessel for the pressure steaming and the degasificaton and gasification process the outlet for the gas is provided between the pressure steaming zone and the after-drying zone.

If the low-temperature carbonization gas and the clear gas are extracted separately it is also possible for both types of gas to be re-combined for the pressure steaming. In this case it is desirable for the clear gas to be freed of dust prior to the said re-combination or for the mixed gas to be freed of dust after the latter and to be saturated with evaporation water. To accelerate the dehydration process in the pressure steaming it is also possible for the crude gas or the gas of the relevant partial flows to be introduced in a superheated state into the pressure steaming chamber.

It is likewise possible for a partial flow of crude gas to be brought to such a high temperature that the phenols accompanying it are destroyed, this partial flow being used for the pressure steaming after saturation with water.

As the crude brown coal or lignite is dried and degasified in a very non-destructive manner by the process to which the present invention relates, a non-disintegrated abrasion-resisting coke can likewise be extracted after the pressure degasification has taken place. To produce a comparatively smokeless solid fuel in this process the degasification, after-drying and optionally the subsequent pressure steaming are carried out with hot scavenging gas, having the maximum steam content, separately from the pressure gasification. The degasified fuel is then cooled and expanded and can be used as coke.

The coke produced or a partial flow thereof can be used for the pressure gasification carried out in a separate chamber, in which case the pressure gas or a separate flow thereof is used for the degasification, after-drying and pressure steaming.

(f) Example: Preferred forms of the invention will be described below in detail by reference to four examples.

Example 1: Crude brown coal or lignite, with a grain size range of 5-60 mm, a water content of 57% by weight and a temperature of about 293 K, is placed in a bunker and heated to about 363" K by means of steam and optionally by the aid of sprayed hot water. From the bunker the crude brown coal or lignite is conveyed into a coal sluice, subjected intermittently to a pressure of 2.5 MPa and sluiced into a vessel for pressure steaming of the crude brown coal or lignite.

In the coal sluice the crude brown coal or lignite is further preheated to 393-423" K with a partial flow of evaporation agent or evaporation water at a temperature of about 490" K.

In the pressure steaming vessel, above the pile of coal or lignite, steam as evaporation agent is supplied at a temperature of 495 K. With the evaporation agent at this temperature it is possible to dehydrate the crude brown coal or lignite to about 25% by H2O in a "steaming time" of 60-90 minutes.

If the crude brown coal or lignite is only dehydrated to a residual water content of about 35% by weight, the steaming time can be reduced to 30-40 minutes.

This enables the pressure steaming vessel to be kept comparatively small. The water dripping off the coal or lignite and removed from the evaporation agent by condensation is separated by a suitable device in the evaporation vessel. In this process the water is accompanied by very fine grain that has formed.

This purification effect is intensified by the spraying of cycled evaporation water, at a temperature of about 490" K in the evaporation vessel. The dehydrated coal or lignite is uniformly heated at 470-500" k and conveyed continuously into a pressure vessel for the after-drying, degasification and gasification, in which vessel the same pressure of 1.5 MPa prevails. By comparison with the method hitherto usual, in which a fuel is supplied at about 303 K and with about 20% by weight H2O, about 370 kJ more heat, per kg of dry coal or lignite, based on 20% by weight H2O, is conveyed with the pressuresteamed coal or lignite into the degasificaton and gasification vessel.This heat suffices to dry the coal or lignite from about 35% to about 20% by weight H2O without withdrawing any heat from the degasification and gasification process. The drying of the coal or lignite is then carried out: to an extend of about 81%, by means of heat from the pressure steaming, of which about 66% is in liquid form in the pressure steaming vessel, and about 15% takes place by evaporation in the pressure degasification and gasification reactor, and to an extent of 19% by evaporation by means of heat from the pressure degasification and gasification process.

As the pieces of coal or lignite enter the degasification and gasification vessel uniformly heated, without any latent water-content margin and without any hardened grain surface due to the influence of the atmosphere, and are after-dried in the said vessel at 2.5 MPa (volume of steam only about 1/21 of that present in the normal atmosphere), this drying takes place without any appreciable damage to the grain of the coal or lignite. The surplus evaporation water, at about 490 K, is expanded to approximately atmospheric pressure. The steam forming, which is at about 373 K, and the water, at the same temperature, serve forth heating of the crude coal or lignite employed to about 363 K.The evaporation agent adopted consists of steam in a saturated state, at 2.5 MPa and about 495 K. If the steam prevailing has a higher pressure and higher temperature it is expanded before entering the evaporation vessel and saturated with evaporation water. The heat required in the said vessel amounts to 1100 kJ per kg of water given off. The supply of steam is regulated in such a way that the CO2 occurring in the pressure carbonization and flowing into the degasification and gasification vessel is always accompanied by a small quantity of residual steam. The evaporation water forming has an extremely low phenol content.

Example 2: Crude brown coal or lignite, with a grain size range of 5-60 mm and a water content of up to 57% by weight is conveyed hydraulically, with evaporation water expanded to atmospheric pressure and having a temperature of 370" K, into a bunker for the gasification plant, being preheated to 363"K in the process. From the bunker it then passes through a coal sluice into a large pressure vessel in the lower part of which the coal or lignite is gasified in the solid bed at a pressure of 2.5 MPa. The gas formed flows upwards in the opposite direction to the coal or lignite and forms the following zones in succession: ash zone, oxidation zone, reduction zone, degasification zone, after-drying zone, steaming zone.

The water dripping out of the crude brown coal or lignite in the pressure steaming zone saturates and supersaturates (by the formation of spray) the ascending crude gas. The surplus evaporation water enters the subsequent zones, from which it takes the heat required for its evaporation. The evaporation of the water may lead to the drawbacks of an increased oxygen and fuel requirement, the worsened disintegration of the gasification steam and an increased proportion of CO2 in the crude gas. With a high proportion of surplus water these drawbacks can be avoided or minimised if devices for separating the pressure water from the coal or lignite are inserted between the pressure steaming zone and the afterdrying zone. With the separated evaporation water some of the fine dust occurring in the evaporation and carried along by the gasification gas is removed.

The evaporation water is expanded and used for the hydraulic transport of the rude coal or lignite to the bunker. The soft brown coal or lignite is dehydrated to a water content of about 35% by weight in the evaporation chamber and after-dried, degasified and gasified in the subsequent zones. The crude gas emerges from the top of the pressure vessel and passes to the waste heat steam generating station. In the present example the crude gas from the degasificaton and gasification process serves, in the steamsaturated state, for the pressure gasification of the solid bed at 2.5 MPa, and about 473" K. The saturated crude gas has a water content of 1.6 kg/m3 i.N. The thermal reqirement in the evaporation zone amounts to about 580 kJ per kg of separated water.

After the steaming process the crude gas has a water content of about 1.3 kg/m3 i.N. and a temperature of about 468 K. The production of waste heat steam (o.5 MPa steam) is limited by the heat given off by the hot crude gas in the steaming process.

Crude gas flows continuously through the pile of coal or lignite, so that the latter is rapidly heated up and the CO2 immediately discharged. The steaming periods involved are thus shortened. Hydrocarbons which have condensed out of the crude gas improve the mobility ofthe pile of material.

The present example may suffer from the drawback that the discharged evaporation water has a high phenol content and subjects the dephenolization plant to a 50% higher load. From the change in the parameters of the crude gas in the evaporation zone it can be seen that only a small proportion of the quantity of steam contained in the crude gas is required for the pressure steaming. It is thus possible to limit the crude gas used for the steaming process to only part of the flow, providing the following variants: (1) A clear gas free of tar and phenol and at a high temperature is extracted from the reduction zone of the solid bed pressure gasification process.

The clear gas is saturated with water, freed of dust as far as necessary and then introduced into the pressure vessel, above the level of the pile of coal or lignite, for the pressure steaming process. It flows in the same direction as the coal through the evaporation zone and leaves the pressure vessel together with the low-temperature carbonization gases, which are conveyed separately, between the pressure steaming and after-drying zone. No additional demands are made on the dephenolization plant by the evaporation water.

(2) When the dust-free low-temperature carbonization gas is used for the pressure steaming process it flows direct, in the opposite direction to the coal or lignite, from the after-drying zone into the pressure steaming zone, where it is saturated by the evaporation water, and emerges from the pressure steaming zone at a point above the level of the pile of coal or lignite. The evaporation water has a high phenol content. The hydrocarbons which have condensed out improve the mobility of the piled material and are to some extent removed from the evaporation water flowing off, together with fine dust which has been washed out.

Example 3: In this example crude brown coal or lignite with a grain size range of 5-12 mm and a water content of up to 57% by weight and preheated to 363" K, is conveyed from the bunker into two pressure vessels alternately. The two pressure vessels perform the following functions in the order shown; Reception of coal or lignite in pressureless state, treatment of crude coal or lignite, with steam, to 10 MPa, dehydration of coal or lignite at 583 K in 15 minutes, down to a water content of 35% by weight by pressure steaming and by removal of the evaporation water, expansion to the pressure of the degasification vessel mounted underneath the pressure vessels, i.e. to 2.5 MPa, and transfer of the coal or lignite into the degasification vessel. The two pressure vessels in alternation supply fuel to the pressure degasification station.

In the degasification vessel the non-destructive after-drying and degasification are carried out with scavenging gas produced by a fluidized bed pressure gasification operation. The coke thus produced is supplied at a measured rate to the fluidized bed gasification process.

After being freed of dust, and in orderto utilize the perceptible and latent heat, the gas generated is conveyed partly as scavenging gas to the degasification process and partly for heating by evolution of the latent heat.

Example 4: In the fourth example crude brown coal or lignite with a grain size range of 40-60 mm and a water content of up to 58% by weight is preheated to 3630 K in a bunker, conveyed into coal sluices, treated with hot water and alternately caused to enter a current of pressure water of 3 a and at 500 K. By means of the pressure water it is conveyed to a pressure steaming station and pre-dehydrated to a water content of 48% by weight in the hydraulic transport operation.

In the pressure steaming vessel the coal or lignite is separated from the transport liquid and afterevaporated, with saturated steam of 2.5 MPa, down to a water content of 35% by weight. The evaporation water flows off together with the conveying liquid and at a temperature of about 485" K. Of this hot water a partial flow, with the fine grain, is separated in a hydrocyclone. The upper flow of the hydrocyclone is restored by means of a pressure increasing pump and a heat exchanger to the parameters 3 MPa and 503" K and once again used for the hydraulic transport of the crude coal or lignite. The coal or lignite predried down to a water content of 35% by water passes from the pressure steaming vessel into a pressure degasification vessel, where it is non-destructively after-dried by means of scavenging gas and degasified to a temperature of 1000 K. The coke produced is cooled, expanded and obtained in the form of comparatively smokeless fuel.

Claims

1. A process for pressure degasificaton and pressure gasification of crude brown coal or lignite, comprising introducing granular crude brown coal or lignite into a pressure steaming chamber at a pressure above 1 MPa, partially dehydrating the brown coal or lignite in the said chamber by means of an evaporation agent, pressure carbonizing, uniformly shrinking and heating it substantially uniformly to a temperature above 423" K and conveying the thus pretreated brown coal or lignite without expansion to a pressure of less than 0.5 MPa into a pressure degasificaton and pressure gasificaton chamber, in which the coal or lignite will undergo further non-destructive drying as a result of its heat content, and subsequently effecting pressure degasification and pressure gasification of the treated brown coal or lignite.

2. A process in accordance with Claim 1, wherein the coal or lignite is soft brown coal or lignite.

3. A process in accordance with Claim 1 or Claim 2, wherein the pressure steaming chamber is at a pressure above 2MPa.

4. A process in accordance with any preceding claim, wherein the said heating of the brown coal or lignite is conducted to a temperature above 453" K.

5. A process in accordance with any preceding claim, wherein the pre-treated brown coal or lignite is conveyed without expansion to a pressure lower than that in the pressure degasification and pressure gasification chamber.

6. A process in accordance with any preceding claim, wherein the pre-treated brown coal or lignite is conveyed into the pressure degasificaton and pressure gasification chamber without cooling down to a temperature of less than 432"K.

7. A process in accordance with Claim 1, wherein the pressure steaming chamber is always maintained at the same temperature as that of the pressure degasification and pressure gasification chamber and the pre-treated coal or lignite passes continuously from the pressure steaming chamber into the pressure degasification and pressure gasification chamber.

8. A process in accordance with any one of Claims 1 to 6, wherein during the pressure steaming operation a pressure which is above 1 MPa prevails in the pressure steaming chamber and after the pre-treatment of the brown coal or lignite the pressure steaming chamber is expanded or compressed to correspond to that of the degasification and gasification chamber and the coal or lignite passes discontinuously into the degasification and gasification chamber.

9. A process in accordance with Claim 8, wherein the pressure steaming is carried out in one or more vessels and the said vessel or vessels sluice(s) the coal or lignite from a presureless bunker in which it is contained into the degasification and gasification chamber subjected to pressure, the process being accompanied, in the pressure steaming chamber and at a preselected rhythm, by expansion to atmospheric pressure, reception of the crude brown coal or lignite, subjecting it to evaporate pressure, pressure steaming and water removal, pressure equalization to the pressure degasificaton and gasificaton chamber and the discharge of the partly dehydrated coal or lignite into the degasification and gasification chamber.

10. A process in accordance with Claim 9, wherein the coal or lignite pre-dehydrated by pressure steaming is after-dried with superheated steam.

11. A process in accordance with Claim 9 or Claim 10, wherein the residual steam leaving a pile of coal or lignite with discharged CO2 in the course of the pressure steaming operaton and the steam flowing off in an after-drying of the coal or lignite with superheated steam are utilized as a gasification agent.

12. A process in accordance with Claim 7, wherein the pressure steaming and the pressure degasification and gasification are carried out in one common pressure vessel.

13. A process in accordance with any preceding claim, wherein water dripping off the coal or lignite in the evaporation chamber frees the coal or lignite of the very fine grain, of which only a small quantity forms, and in order to intensify this cleaning effect recycled evaporation water is sprayed in an evaporation chamber, above the level of a pile of coal or lignite.

14. A process in accordance with any preceding claim, wherein evaporation water is continuously separated in an evaporation chamber and conveyed to a steam or hot water generating station.

15. A process in accordance with any preceding claim, wherein evaporation water is expanded to atmospheric pressure and that the resulting steam and/or hot water is used for the pre-heating of the crude brown coal or lignite.

16. A process in accordance with any preceding claim, wherein expanded hot water is utilized for the hydraulic transport of the crude brown coal or lignite to the bunker or other coal or lignite containing receptacle preceding the process, the crude brown coal or lignite being at the same time heated.

17. A process in accordance with any one of Claims 1 to 8, or any one of Claims 12 to 14, wherein evaporation water separated under pressure is utilized for hydraulic transport of the crude brown coal or lignite from a coal sluice to the pressure steaming chamber, the process being accompanied by a preliminary steaming of the coal or lignite.

18. A process in accordance with any one of Claims 1 to 8 or any one of Claims 12 to 15 or Claim 17, wherein the crude brown coal or lignite is heated up in advance in a coal sluice by means of a partial flow of evaporation agent and/or hot evaporation water.

19. A process in accordance with any preceding claim, wherein steam saturated for pressure steaming and optionally slightly superheated is conveyed into an evaporation chamber.

20. A process in accordance with any preceding claim, wherein the evaporation agent consists of steam which is saturated with evaporation water at the selected saturation pressure and is conveyed into a saturation chamber, at a level above a pile of the coal or lignite, in a quantity which ensures that a slight amount of residual steam flows into the degasification and gasification chamber together with the gases which have formed in the carbonization of the coal or lignite.

21. A process in accordance with any one of Claims 1 to 6, Claim 7 or any one of Claims 12 to 20, wherein casing steam which has been produced in a water jacket of the pressure degasification and gasificaton vessel is used for the pressure steaming process.

22. A process in accordance with any one of Claims 1 to 18, wherein pressure steaming of granular crude brown coal or lignite with hot saturated or only slightly superheated gases containing steam and coming from partial oxidation of fuels is effected under pressure and with a partial steam pressure of over 1 MPa, the hot gas containing steam flowing continuously through the coal or lignite to be dehydrated, the amount of steam carried along by the gas and condensing out in the pressure steaming process being limited to the amount at which the partial steam pressure will still be at least 0.5 MPa, while the gas containing steam also causes the gases occurring in the pressure carbonization to leave the pressure steaming chamber and accelerates the process of lyopolar and capillary release of water.

23. A process in accordance with any one of Claims 1 to 7, Claim 12 or Claim 22, wherein the pressure steaming, non-destructive after-drying, degasification and gasification are carried out in a pressure vessel, while the crude gas produced by pressure gasification in the lower part of the vessel flows upwards in the opposite direction to the flow of coal or lignite, in which process it effects the degasification, non-destructively after drying and pressure steaming in a pile of coal or lignite in zones which succeed one another directly.

24. A process in accordance with any one of Claims 1 to 7, Claim 12, Claim 22 or Claim 23, wherein by means of crude gas some of the water given off by the crude brown coal or lignite in the pressure steaming process is conveyed out of the pressure vessel in the form of fine drops.

25. A process in accordance with any one of Claims 1 to 7, any one of Claims 12 to 18 or any one of Claims 22 to 24, wherein water dripping off the coal or lignite is separated by means of suitable devices between evaporation zones and after-drying zones.

26. A process in accordance with Claim 22, wherein gas containing steam and coming from partial oxidation of fuels is saturated before being conveyed into an evaporation chamber and is freed of entrained dust and of condensed hydrocarbons.

27. A process in accordance with any one of Claims 22 to 25, wherein in the cooling of the gas containing steam, hydrocarbons which have condensed out in the course of the steaming process improve the mobility of the coal or lignite to be dehydrated.

28. A process in accordance with any one of Claims 22 to 27, wherein crude gas containing steam and used for the pressure steaming is saturated by the water separated from the coal or lignite in the pressure steaming process and is freed of dust.

29. A process in accordance with Claim 22 or any one of Claims 24 to 28, wherein when use is made of hot gases containing steam and coming from partial oxidation of fuels free of phenol and of superheated gases containing steam the said gases are introduced into an evaporation chamber at a point above the level of a pile of the coal or lignite.

30. A process in accordance with any one of Claims 22 to 25, wherein in the degasification and gasification chamber only part of the flow of crude gas produced in the degasification and gasification chamber is used for further non-destructive afterdrying and degasification of the grains predehydrated by pressure steaming.

31. A process in accordance with any one of Claims 22 to 25 or Claim 27 or Claim 28, wherein a partial flow of gas with which the non-destructive after-drying and degasification are carried out and which contains only little dust but a large quantity of hydrocarbons is subsequently used for the pressure steaming of the grains of crude coal.

32. A process in accordance with Claim 22 or any one of Claims 24 to 26 or Claim 28 or Claim 29, wherein a partial flow of the crude gas generated in the degasification and gasification chamber is extracted from the reduction zone in the form of a tar-free clear gas and is then used for the pressure steaming of the crude brown coal or lignite after saturation and after any necessary removal of dust.

33. A process in accordance with any one of Claims 22, 24, 25, 28, 29 or Claim 32, wherein clear gas is extracted from the reduction zone at the appropriate temperature or a partial flow of crude gas is brought to a sufficiently high temperature to ensure that steam accompanying the gas is free of phenol before it is conveyed into an evaporation zone.

34. A process in accordance with any one of Claims 22, 23, 27, to 29 or 31 to 33, wherein after pressure steaming or granular crude brown coal or lignite, with hot gases containing steam and coming from the parial oxidation of fuels, the dehydrated grains are expanded and they put to further use as required.

35. A process in accordance with any one of Claims 1 to 11, to 22, 24 to 27,28,29,32 or 33, wherein the pressure gasification process is carried out by a separating dosing device or in a separate vessel from the operations of pressure steaming, after-drying and degasification.

36. A process in accordance with any one of Claims 1 to 11, to 22, to 26, 28, 29,32,33or35, wherein coke obtained after the pressure degasification process is obtained in a cooled and expanded state and in the form of a comparatively smokeless fuel.

37. A process in accordance with any one of Claims 1 to 11, to 22, 24 to 26,28,29,32,33, 35 to 36, wherein coke produced or only part of this quantity undergoes a separate pressure gasification and that the gas thus produced or part thereof is utilized as scavenging gas for the gasification, after-drying and pressure steaming.

38. A process in accordance with any one of Claims 1 to 13to 22,24to26,28, 26,28,29,32,33to 35 to 37, wherein in the pressure steaming some of the ash is removed from the coal or !ignite, the ash content of the coke thus produced being therefore comparatively slight.

39. A process in accordance with Claim 1 substantially as herein described and exemplified.