CA1213844A - Production of beneficiated lignite and brown coals - Google Patents
Production of beneficiated lignite and brown coalsInfo
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- CA1213844A CA1213844A CA000451992A CA451992A CA1213844A CA 1213844 A CA1213844 A CA 1213844A CA 000451992 A CA000451992 A CA 000451992A CA 451992 A CA451992 A CA 451992A CA 1213844 A CA1213844 A CA 1213844A
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
- C10L9/00—Treating solid fuels to improve their combustion
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- Combustion & Propulsion (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Organic Chemistry (AREA)
- Solid Fuels And Fuel-Associated Substances (AREA)
Abstract
PRODUCTION OF BENEFICIATED LIGNITIC AND BROWN COALS
Abstract This invention relates to a process and apparatus for the beneficiation of lignitic and brown coals, in which water, alkali metals and sulphur contents of the original coal are substantially reduced, the dry basis heating value is increased and the tendency for spontaneous combustion is substantially eliminated. The treatment involves contacting the coals in slurry form with saturated steam for up to one hour, at temperatures between 250 and 374°C at corresponding steam pressures. The product coal is cleaner burning, easier, safer and cheaper to transport, thereby resulting in capital, operating and maintenance cost savings.
Abstract This invention relates to a process and apparatus for the beneficiation of lignitic and brown coals, in which water, alkali metals and sulphur contents of the original coal are substantially reduced, the dry basis heating value is increased and the tendency for spontaneous combustion is substantially eliminated. The treatment involves contacting the coals in slurry form with saturated steam for up to one hour, at temperatures between 250 and 374°C at corresponding steam pressures. The product coal is cleaner burning, easier, safer and cheaper to transport, thereby resulting in capital, operating and maintenance cost savings.
Description
PRODUCTION OF BENEFICIATED LIGNITIC AND BROWN COALS
Field of the Invention This invention is directed to a novel process and apparatus for beneEiciating lignitic and brown coals to a low moisture, low sodium, low sulphur form that is useul for combustion or for conversion to clean gaseous or liquid fuels.
Back~round of the Invention Due to the rising demand and diminishing supply of premium natural resource fuels such as oil and natural gas, a human need has arisen for the efficient and economic utilization of heretoore largely ignored lower grade natural resource fuels such as lignite and brown coal. These lower grade fuels for purposes of use by man sufer from many shortcomings. One is inherent high water contents ranging from 30-80 percent in the as-mined coals. This water must be substantially driven off before the substance can be used as fuel. A second shortcoming is a dangerous acquired tendency towards spontaneous combustion when such partially dried coals readsorb moisture from the air.
A number of processes have been demonstrated in the prior art for the removal of moisture from lignite and brown coals. One process involves heating the coal in oil to dehydrate the coal. ~ major difficulty with this process is that it leaves a residue of about 10 percent oil in the coal, which increases greatly the cost of the process, while defeating the main purpose of the process, that i6, to decrease the use of premium fuels.
Another process involves briquetting the coal with an asphalt binder to prevent spontaneous combus-tion. This process produces a dirtier burning coal by-the addition of sulphur originally contained in the asphalt.
Other taught processes use evaporative tech-niques to dry the coal. These processes are costly due to high energy usage, do not prevent spontaneous com-bustion in the product, and generally degrade the product with respect to particle size and strength.
Applicant's co-pending Canadian pa-tent application Serial No. 378,8~2, filed June 2, 1981, B.D. Kybett, A.J. Szladow, A. Verma, and L.W. Vigrass, entitled "~pparatus and Process for Dewatering and Beneficiating Lignite", discusses in detail the background in this field and discloses and claims a process and apparatus for dewatering and beneficiating the quality o~ lignite by fluidizing crushed and particulated raw lignite and passing steam through the fluidized iignite.
Summar~ o~ the Invention This invention relates to a process for the beneficiating of lignitic and brown coals, whereby the water, alkali metals and sulphur contents of the origi-nal coal are substantially reduced, and dry basis heating value is increased.
It has been discovered that, by contacting crushed lignite and brown coals under sui-table condi-8~
tions of time, temperature and pressure, with saturatedsteam, the coal produeed has a substantially reduced content of equilibrium moisture, sulphur and alkali metals. In addition, the produced coals are not prone to spontaneous combustion, are less dusty than those obtained with prior processes, retain their original hardness, and have increased dry basis heating value.
In most cases, it has been found, the reduc-tion in sulphur content which results from treatment n with our process is sufficient to make the use of flue gas desulphurization unnecessary when the product coal is burned. We have also found that maintenance, capital and operating costs on boilers firing coal treated to our proeess are substantially reduced due to a reduetion in alkali metals eontent. Lower alkali metals content lessens problems related to slagging and fouling.
Further benefits, we have diseovered~ are that our treated eoals are more eeonomical to transport due to reduced moisture eontent, are eleaner due to reduced dustiness, and are sarer to use due to a redueed ~endency toward spontaneous combustion.
The invention involves a process and apparatus for the benefieiation of raw lignitie or brown coal, to produee a eoal of redueed water, alkali metal and sulphur content, redueed spontaneous combustion tend-eney, and heating value eomprising: (a) erushing, grinding and sizing the ra~ lignitie and brown coal; (b) direeting the coal obtained from step (a) to a slurry preparation faeility where the coal is slurried with water; ~e) directing the slurry obtained from step (b) ~38~9~
to a reactor in which the coal slurry is contacted for a period of up to one hour with saturated steam at a temperature in the range 250C to 374C, and a pressure in the range 4 MPa to 22 MPa.
The product obtained from step tc) is then directed to first phase separation means. Subsequently, the product obtained from the first phase separation is directed to a second phase separation means which operates at a lower pressure than the first phase separation means.
Reactor of step (c) operates in an ebullated bed mode, and saturated steam acts as a Eluidizing medium for the slurried lignitic and brown coal. The reactor may operate at a temperature of 350C and a pressure of 16.5 MPa with a contact time of 5 minutes, using coal slurried with water, or at a temperature of 275C and a pressure of 6 MPa with a contact time of 12 minutes, using coal slurried with water. The first phase separation means may be at least one hydrocyclone which separa-tes the coal slurry into an over 50 percent coal stream and an under 1 percent coal stream. Means for relieving the pressure between the first phase separation means and the second phase separation means may be included.
Drawings FIGURE 1 represents a block diagram flow sheet illustrating the subject process for converting raw lig-nitic and brown coals to cleaner, saEer, drier fuels.
Detailed Description of the Invention In the practice of the invention, run-of-mine lignitic or brown coal is passed through crushing, ~1, _ grinding and sizing facilities Erom which it exits in a size range suitable Eor the preparation and pumping of a slurry. In a preferred embodiment ~f this invention, coal is sized to a range of 5 mm X 0.3 mm and is slurried with water in a 50:50 ratio. The minus 0.3 mm fraction is used either to feed the process steam boiler, or is sold as a by-product. In a further pre~erred embodimentt screening is carried out using a dry Rodeck~-type screen to Eacilitate this operation.
Sized coal is conveyed to a slurry preparation area where it is mixed with a suitable fluid medium in proportions suitable for pumping by means of high pressure slurry pumps to the reactor area.
The reactor is a suitably strong vessel capable of withstanding the combination of high temper-ature, high pressure and abrasive particles, while providing efficient contact between the coal slurry and saturated steam. Usual operating conditions in the reactor consist of temperatures in the range of 250C to 374C, corresponding saturated steam pressures in the range of 4 MPa to 22 MPa, and retention times up to 1 hour. ~n preferred embodiments of the invention, the reaction conditions are, depending on the type OL coal employed, 350C at 16.5 MPa for 5 minutes, or 275C at 6 MPa for 12 minutes. Contacting of the coal slurry with the saturated steam may be carried out by any suitable conventional means. In a preferred embodiment of the invention, the reactor is of the ebullated bed type with steam acting as the fluidizing medium. Appropriate velocity and cross-sectional areas are chosen to produce the required retention time.
Steam is produced for the reaction by any suitable means. ~ boiler may be fired by natural gas, or in the preferred embodiment of the invention, by surplus minus 0.3 mm coal fines from the screening facility.
Upon exiting the reactor, the treated coal slurry enters a phase separating apparatus. Without steam treatment, such means for phase separation would be unsuccessful in the removal of water, since chemlcal bonds exist which hold the water in the pores of the coal. ~fter treatment with steam, these bonds are broken, and some of the pores are shrunk, thereby permitting water removal by any suitable means. This phase separation occurs at the prescribed reaction pressure to prevent evaporation, energy inefficiencies and degradation of the coal particles~ In a preferred embodiment of the invention, a bank of hydrocyclones is emplo~ed to separate the slurry feed into two streams, one having over 50 percent coal, the other having less than 1 percent coal.
These streams are cooled by passing them through heat exchangers after which they enter means for pressure letdown. In a preferred embodiment of the invention, the less than 1 percent coal stream is depressurized using an impulse turbine, which also recovers pressure energy. The greater than 50 percent coal stream is depressurized in two stages by pressure letdown valves and pressure vessels.
3LZ~3~
After pressure let-down, fur-ther heat exchange occurs, and the streams then enter a second phase separating area, which operates at a lower pressure than the Eirst phase separating means. In a preferred embodiment of the invention, the greater than 50 percent coal stream is fraction separated in a bank of solid bowl centrifuges, with the process water from the centrifuges being passed through gravity screens. The less than 1 percent coal stream is passed directly to n the gravity screens for phase separation.
Suitable pumpi~g means are employed in the treating facility to propel the streams through the plant. In a preferred embodiment of this invention, the slurry is moved first through low-pressure centrifugal pumps and then through high-pressure, positive displace-ment, slurry pumps.
For reasons of economy and efficiency, energy recovery is an important consideration of this treatment process, and suitable heat e~change means, Eamiliar to those skilled in the art, are employed to heat the incoming streams and cool the outgoing streamsO
Solid, liquid and gaseous effluen~ streams are treated such that they are suitable for environmentally acceptable disposal, for recycle purposes, and/or for ~5 the recovery of process heatO Appropriate conventional means may be used for these purposes. Liquid streams may be passed through tilted plate coalescers to remove any organics which may be further processed or burned for process heat. Gaseous streams may be passed through a Stretford plant, with sulphur recovered as a by-- ~X~3~
product. Water produced by the process may be sent to a wastewater treatment facility consisting of sedimenta-tion, activated slud~e, aeration and chlorination.
Alternatively, process heat and steam may be generated in a wet air oxidation unit.
The process and apparatus of the invention will now be discussed with specific reference to the drawing. FIGURE 1, which depicts a blok diagram of a proposed plant, describes a pre~erred embodiment of the process and apparatus o:E this invention. Referring to FIGURE 1, lignitic coal 1 is prepared in the coal crushing, grinding and sizing facilities 2 and excess coal fines are either used to fire the boiler 3 or are sold as a by-product 4. The prepared coal obtained from facility 2 is slurried with water in the slurry prepara-tion area 5 and is then pumped in series through heat exchangers 6, 7 and 8 to the reactors 9. Steam produced in the boiler 3 also enters the reactors 9 and fluidizes the coal slurry. After a suitable retention time at operating temperature and pressure, the treated lignitic slurry enters phase separating means, consisting of a bank of hydrocyclones 10, and is separated into two streams, a 60 percent coal slurry 11 and a 0.5 percent coal slurry 12. The 60 percent coal slurry 11 is passed through heat e~changer 13 and enters a pressure letdown system 14, in this case a pressure letdown valve, which is followed by a flash vessel 15. This stream is then further separated by means of a bank of solid bowl centrifuges 16. Following surface evaporation 17, the beneficiated lignite enters the product loadout area 18.
The 0.5 percent coal slurry 12 is passed through heat exchanger 19, and then enters a pressure letdown system 20, in this case, an impulse turbine which generates power 21 .~rom the pressure energy.
Organics are separated from the waste water by suitable conventional means 22 and are pumped to the by-product loadout area 23. Waste water from the solid bowl centrifuges 16 is also treated in a suitable system 24 to remove organics, and the organics are sent to the by-product loadout area 23.
Waste water from organics separation means 22 is passed through a 1ash vessel 25 and the.~ through heat exchanger 26. The waste water from organic separation means 24 is passed through heat exchanger 27 and both waste water streams are then passed through gravity screens 28 and 29 with further separated product entering surface moisture evaporation area 17 and then to the product loadout area 18. Waste water then enters the waste wa~er treatment area 30~ Some of the treated water is recycled after being held in the recycle water pond 31. Surplus water from area 30 is disposed of via area 32, while waste sludge enters waste sludge lagoon 33.
O~f-gases and steam from the reactors 9 enter a pressure reduction stage 34. Pressure energy is recovered by steam turbine 35 and power is generated at generator 36. The gases from turbine 35 pass through a heat exchanger 37 and condensed steam is sent to the g _ boiler feedwater treatment area 38. Off-gases are compressed at compressor 39 and then enter the Stretford gas treatmen plant 40. Recovered sulphur from plant 40 passes to by-product loadout area 41 while flue gas from plant 40 is re-heated at stage 42 and then vented to atmosphere through stack 43.
Off-gases from the boiler 3 enter an electro-static precipitator 44 with the obtained flyash being sent to flyash lagoon ~5. Flue gas is desulphurized at stage 46 and the sludge that is produced is disposed of at sludge lagoon 47. Bottom ash from boiler 3 is transmitted to bottom ash lagoon 48.
Other treatment zones and streams appearing on FIGURE 1 are believed to be self-evident and should not require detailed discussion.
The following example illustrates a process according to this inven-tion:
Example A typical Saskatchewan water bearing lignite was treated in a small batch version of the process of this invention. Treatment was carried out at 350C at 16.5 MPa steam pressure for 5 minutes, using a water slurry medium.
The coal feed had the following properties:
moisture content as-received - 35.5 percent;
equilibrium moisture - 33.5 percent;
heating value, dry basis - 24.66 MJ/kg, sulphur content - 0.47 percent (dry basis);
Na2O - 2.27 percent of ash.
12~
Dustiness, spontaneous combustion and slaking were highO
After 5 minutes of treatment in the process of this invention, the resultant coal had the following properties:
equilibrium moisture - 14.8 percent;
heating value, dry basis - 26.21 MJ/kg;
sulphur content - 0.21 percent (dry basis);
Na2O - 1.07 percent of ash.
Dustiness and slaking were slight, and there was no tendency for spontaneous combustion.
It is speculated that the reason for the success of the subject process is that the steam treat-ment under the conditions prescribed is able to break chemical bonds which hold inherent moisture in ~he pores of the coal. As well, it is believed the saturated steam acts as a solvent for leaching alkali metals.
Chemical bonds which are broken are also believed to release sulphur, ar.d carbon dioxide, thereby resulting in an increase in heating value. As well, surFace pores are believed to be collapsed, thereby effectively sealing the surface from subsequent moisture readso~p-tion and thus preventing spontaneous combustion.
As will be apparent to those skilled in theart in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the ~Z~3~
invention is to be construed in accordance with the substance defined by the following claims.
- 12 ~
Field of the Invention This invention is directed to a novel process and apparatus for beneEiciating lignitic and brown coals to a low moisture, low sodium, low sulphur form that is useul for combustion or for conversion to clean gaseous or liquid fuels.
Back~round of the Invention Due to the rising demand and diminishing supply of premium natural resource fuels such as oil and natural gas, a human need has arisen for the efficient and economic utilization of heretoore largely ignored lower grade natural resource fuels such as lignite and brown coal. These lower grade fuels for purposes of use by man sufer from many shortcomings. One is inherent high water contents ranging from 30-80 percent in the as-mined coals. This water must be substantially driven off before the substance can be used as fuel. A second shortcoming is a dangerous acquired tendency towards spontaneous combustion when such partially dried coals readsorb moisture from the air.
A number of processes have been demonstrated in the prior art for the removal of moisture from lignite and brown coals. One process involves heating the coal in oil to dehydrate the coal. ~ major difficulty with this process is that it leaves a residue of about 10 percent oil in the coal, which increases greatly the cost of the process, while defeating the main purpose of the process, that i6, to decrease the use of premium fuels.
Another process involves briquetting the coal with an asphalt binder to prevent spontaneous combus-tion. This process produces a dirtier burning coal by-the addition of sulphur originally contained in the asphalt.
Other taught processes use evaporative tech-niques to dry the coal. These processes are costly due to high energy usage, do not prevent spontaneous com-bustion in the product, and generally degrade the product with respect to particle size and strength.
Applicant's co-pending Canadian pa-tent application Serial No. 378,8~2, filed June 2, 1981, B.D. Kybett, A.J. Szladow, A. Verma, and L.W. Vigrass, entitled "~pparatus and Process for Dewatering and Beneficiating Lignite", discusses in detail the background in this field and discloses and claims a process and apparatus for dewatering and beneficiating the quality o~ lignite by fluidizing crushed and particulated raw lignite and passing steam through the fluidized iignite.
Summar~ o~ the Invention This invention relates to a process for the beneficiating of lignitic and brown coals, whereby the water, alkali metals and sulphur contents of the origi-nal coal are substantially reduced, and dry basis heating value is increased.
It has been discovered that, by contacting crushed lignite and brown coals under sui-table condi-8~
tions of time, temperature and pressure, with saturatedsteam, the coal produeed has a substantially reduced content of equilibrium moisture, sulphur and alkali metals. In addition, the produced coals are not prone to spontaneous combustion, are less dusty than those obtained with prior processes, retain their original hardness, and have increased dry basis heating value.
In most cases, it has been found, the reduc-tion in sulphur content which results from treatment n with our process is sufficient to make the use of flue gas desulphurization unnecessary when the product coal is burned. We have also found that maintenance, capital and operating costs on boilers firing coal treated to our proeess are substantially reduced due to a reduetion in alkali metals eontent. Lower alkali metals content lessens problems related to slagging and fouling.
Further benefits, we have diseovered~ are that our treated eoals are more eeonomical to transport due to reduced moisture eontent, are eleaner due to reduced dustiness, and are sarer to use due to a redueed ~endency toward spontaneous combustion.
The invention involves a process and apparatus for the benefieiation of raw lignitie or brown coal, to produee a eoal of redueed water, alkali metal and sulphur content, redueed spontaneous combustion tend-eney, and heating value eomprising: (a) erushing, grinding and sizing the ra~ lignitie and brown coal; (b) direeting the coal obtained from step (a) to a slurry preparation faeility where the coal is slurried with water; ~e) directing the slurry obtained from step (b) ~38~9~
to a reactor in which the coal slurry is contacted for a period of up to one hour with saturated steam at a temperature in the range 250C to 374C, and a pressure in the range 4 MPa to 22 MPa.
The product obtained from step tc) is then directed to first phase separation means. Subsequently, the product obtained from the first phase separation is directed to a second phase separation means which operates at a lower pressure than the first phase separation means.
Reactor of step (c) operates in an ebullated bed mode, and saturated steam acts as a Eluidizing medium for the slurried lignitic and brown coal. The reactor may operate at a temperature of 350C and a pressure of 16.5 MPa with a contact time of 5 minutes, using coal slurried with water, or at a temperature of 275C and a pressure of 6 MPa with a contact time of 12 minutes, using coal slurried with water. The first phase separation means may be at least one hydrocyclone which separa-tes the coal slurry into an over 50 percent coal stream and an under 1 percent coal stream. Means for relieving the pressure between the first phase separation means and the second phase separation means may be included.
Drawings FIGURE 1 represents a block diagram flow sheet illustrating the subject process for converting raw lig-nitic and brown coals to cleaner, saEer, drier fuels.
Detailed Description of the Invention In the practice of the invention, run-of-mine lignitic or brown coal is passed through crushing, ~1, _ grinding and sizing facilities Erom which it exits in a size range suitable Eor the preparation and pumping of a slurry. In a preferred embodiment ~f this invention, coal is sized to a range of 5 mm X 0.3 mm and is slurried with water in a 50:50 ratio. The minus 0.3 mm fraction is used either to feed the process steam boiler, or is sold as a by-product. In a further pre~erred embodimentt screening is carried out using a dry Rodeck~-type screen to Eacilitate this operation.
Sized coal is conveyed to a slurry preparation area where it is mixed with a suitable fluid medium in proportions suitable for pumping by means of high pressure slurry pumps to the reactor area.
The reactor is a suitably strong vessel capable of withstanding the combination of high temper-ature, high pressure and abrasive particles, while providing efficient contact between the coal slurry and saturated steam. Usual operating conditions in the reactor consist of temperatures in the range of 250C to 374C, corresponding saturated steam pressures in the range of 4 MPa to 22 MPa, and retention times up to 1 hour. ~n preferred embodiments of the invention, the reaction conditions are, depending on the type OL coal employed, 350C at 16.5 MPa for 5 minutes, or 275C at 6 MPa for 12 minutes. Contacting of the coal slurry with the saturated steam may be carried out by any suitable conventional means. In a preferred embodiment of the invention, the reactor is of the ebullated bed type with steam acting as the fluidizing medium. Appropriate velocity and cross-sectional areas are chosen to produce the required retention time.
Steam is produced for the reaction by any suitable means. ~ boiler may be fired by natural gas, or in the preferred embodiment of the invention, by surplus minus 0.3 mm coal fines from the screening facility.
Upon exiting the reactor, the treated coal slurry enters a phase separating apparatus. Without steam treatment, such means for phase separation would be unsuccessful in the removal of water, since chemlcal bonds exist which hold the water in the pores of the coal. ~fter treatment with steam, these bonds are broken, and some of the pores are shrunk, thereby permitting water removal by any suitable means. This phase separation occurs at the prescribed reaction pressure to prevent evaporation, energy inefficiencies and degradation of the coal particles~ In a preferred embodiment of the invention, a bank of hydrocyclones is emplo~ed to separate the slurry feed into two streams, one having over 50 percent coal, the other having less than 1 percent coal.
These streams are cooled by passing them through heat exchangers after which they enter means for pressure letdown. In a preferred embodiment of the invention, the less than 1 percent coal stream is depressurized using an impulse turbine, which also recovers pressure energy. The greater than 50 percent coal stream is depressurized in two stages by pressure letdown valves and pressure vessels.
3LZ~3~
After pressure let-down, fur-ther heat exchange occurs, and the streams then enter a second phase separating area, which operates at a lower pressure than the Eirst phase separating means. In a preferred embodiment of the invention, the greater than 50 percent coal stream is fraction separated in a bank of solid bowl centrifuges, with the process water from the centrifuges being passed through gravity screens. The less than 1 percent coal stream is passed directly to n the gravity screens for phase separation.
Suitable pumpi~g means are employed in the treating facility to propel the streams through the plant. In a preferred embodiment of this invention, the slurry is moved first through low-pressure centrifugal pumps and then through high-pressure, positive displace-ment, slurry pumps.
For reasons of economy and efficiency, energy recovery is an important consideration of this treatment process, and suitable heat e~change means, Eamiliar to those skilled in the art, are employed to heat the incoming streams and cool the outgoing streamsO
Solid, liquid and gaseous effluen~ streams are treated such that they are suitable for environmentally acceptable disposal, for recycle purposes, and/or for ~5 the recovery of process heatO Appropriate conventional means may be used for these purposes. Liquid streams may be passed through tilted plate coalescers to remove any organics which may be further processed or burned for process heat. Gaseous streams may be passed through a Stretford plant, with sulphur recovered as a by-- ~X~3~
product. Water produced by the process may be sent to a wastewater treatment facility consisting of sedimenta-tion, activated slud~e, aeration and chlorination.
Alternatively, process heat and steam may be generated in a wet air oxidation unit.
The process and apparatus of the invention will now be discussed with specific reference to the drawing. FIGURE 1, which depicts a blok diagram of a proposed plant, describes a pre~erred embodiment of the process and apparatus o:E this invention. Referring to FIGURE 1, lignitic coal 1 is prepared in the coal crushing, grinding and sizing facilities 2 and excess coal fines are either used to fire the boiler 3 or are sold as a by-product 4. The prepared coal obtained from facility 2 is slurried with water in the slurry prepara-tion area 5 and is then pumped in series through heat exchangers 6, 7 and 8 to the reactors 9. Steam produced in the boiler 3 also enters the reactors 9 and fluidizes the coal slurry. After a suitable retention time at operating temperature and pressure, the treated lignitic slurry enters phase separating means, consisting of a bank of hydrocyclones 10, and is separated into two streams, a 60 percent coal slurry 11 and a 0.5 percent coal slurry 12. The 60 percent coal slurry 11 is passed through heat e~changer 13 and enters a pressure letdown system 14, in this case a pressure letdown valve, which is followed by a flash vessel 15. This stream is then further separated by means of a bank of solid bowl centrifuges 16. Following surface evaporation 17, the beneficiated lignite enters the product loadout area 18.
The 0.5 percent coal slurry 12 is passed through heat exchanger 19, and then enters a pressure letdown system 20, in this case, an impulse turbine which generates power 21 .~rom the pressure energy.
Organics are separated from the waste water by suitable conventional means 22 and are pumped to the by-product loadout area 23. Waste water from the solid bowl centrifuges 16 is also treated in a suitable system 24 to remove organics, and the organics are sent to the by-product loadout area 23.
Waste water from organics separation means 22 is passed through a 1ash vessel 25 and the.~ through heat exchanger 26. The waste water from organic separation means 24 is passed through heat exchanger 27 and both waste water streams are then passed through gravity screens 28 and 29 with further separated product entering surface moisture evaporation area 17 and then to the product loadout area 18. Waste water then enters the waste wa~er treatment area 30~ Some of the treated water is recycled after being held in the recycle water pond 31. Surplus water from area 30 is disposed of via area 32, while waste sludge enters waste sludge lagoon 33.
O~f-gases and steam from the reactors 9 enter a pressure reduction stage 34. Pressure energy is recovered by steam turbine 35 and power is generated at generator 36. The gases from turbine 35 pass through a heat exchanger 37 and condensed steam is sent to the g _ boiler feedwater treatment area 38. Off-gases are compressed at compressor 39 and then enter the Stretford gas treatmen plant 40. Recovered sulphur from plant 40 passes to by-product loadout area 41 while flue gas from plant 40 is re-heated at stage 42 and then vented to atmosphere through stack 43.
Off-gases from the boiler 3 enter an electro-static precipitator 44 with the obtained flyash being sent to flyash lagoon ~5. Flue gas is desulphurized at stage 46 and the sludge that is produced is disposed of at sludge lagoon 47. Bottom ash from boiler 3 is transmitted to bottom ash lagoon 48.
Other treatment zones and streams appearing on FIGURE 1 are believed to be self-evident and should not require detailed discussion.
The following example illustrates a process according to this inven-tion:
Example A typical Saskatchewan water bearing lignite was treated in a small batch version of the process of this invention. Treatment was carried out at 350C at 16.5 MPa steam pressure for 5 minutes, using a water slurry medium.
The coal feed had the following properties:
moisture content as-received - 35.5 percent;
equilibrium moisture - 33.5 percent;
heating value, dry basis - 24.66 MJ/kg, sulphur content - 0.47 percent (dry basis);
Na2O - 2.27 percent of ash.
12~
Dustiness, spontaneous combustion and slaking were highO
After 5 minutes of treatment in the process of this invention, the resultant coal had the following properties:
equilibrium moisture - 14.8 percent;
heating value, dry basis - 26.21 MJ/kg;
sulphur content - 0.21 percent (dry basis);
Na2O - 1.07 percent of ash.
Dustiness and slaking were slight, and there was no tendency for spontaneous combustion.
It is speculated that the reason for the success of the subject process is that the steam treat-ment under the conditions prescribed is able to break chemical bonds which hold inherent moisture in ~he pores of the coal. As well, it is believed the saturated steam acts as a solvent for leaching alkali metals.
Chemical bonds which are broken are also believed to release sulphur, ar.d carbon dioxide, thereby resulting in an increase in heating value. As well, surFace pores are believed to be collapsed, thereby effectively sealing the surface from subsequent moisture readso~p-tion and thus preventing spontaneous combustion.
As will be apparent to those skilled in theart in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the ~Z~3~
invention is to be construed in accordance with the substance defined by the following claims.
- 12 ~
Claims (18)
1. A process for the beneficiation of raw lignitic or brown coal, to produce a coal of reduced water, alkali metal and sulphur content, reduced spontaneous combustion tendency, and increased dry basis heating value comprising:
(a) crushing, grinding and sizing the raw lignitic or brown coal;
(b) directing the coal obtained from step (a) to a slurry preparation facility where the coal is slurried with water; and (c) directing the slurry obtained from step (b) to a reactor in which the coal slurry is contacted for a period of up to one hour with saturated steam at a temperature in the range 250°C to 374°C, and a pressure in the range 4 MPa to 22 MPa.
(a) crushing, grinding and sizing the raw lignitic or brown coal;
(b) directing the coal obtained from step (a) to a slurry preparation facility where the coal is slurried with water; and (c) directing the slurry obtained from step (b) to a reactor in which the coal slurry is contacted for a period of up to one hour with saturated steam at a temperature in the range 250°C to 374°C, and a pressure in the range 4 MPa to 22 MPa.
2. A process according to Claim 1 wherein the product obtained from the reactor is directed to a first phase separation means.
3. A process according to Claim 2 wherein the product obtained from the first phase separation means is directed to a second phase separation means which operates at a lower pressure than the first phase separation means.
4. A process according to Claim 1, 2 or 3 wherein the reactor operates in an ebullated bed mode, and saturated steam acts as a fluidizing medium for the slurried lignitic or brown coal.
5. A process according to Claim 1, 2 or 3 wherein the steam is generated in a steam generating facility comprising a lignite-fired boiler, fed by lignite fines obtained from the crushing, grinding and sizing facility.
6. A process according to Claim 2 wherein the first phase separation means is at least one hydrocyclone, which separates the coal slurry into an over 50 percent coal stream and an under 1 percent coal stream.
7. A process according to Claim 3 including means for relieving the pressure between the first phase separation means and the second phase separation means.
8. A process according to Claim 7 wherein the pressure relief means consists of an impulse turbine which recovers pressure energy from the pressurized stream.
9. A process according to Claim 1, 2 or 3 wherein the reactor operates at a temperature of about 350°C and a pressure of about 16.5 MPa with a contact time of about 5 minutes.
10. A process according to Claim 1, 2 or 3 wherein the reactor operates at a temperature of about 275°C and a pressure of about 6 MPa with a contact time of about 12 minutes.
11. An apparatus for the beneficiation of lignitic or brown coal, wherein water, alkali metal and sulphur content of the coal are substantially reduced, dry basis heating value is increased, and spontaneous combustion tendency of the resultant coal is reduced, comprising:
(a) coal crushing, grinding and sizing means;
(b) ground coal/water slurry preparation means;
(c) steam generating means; and (d) reactor means in which coal slurry is contacted with saturated steam.
(a) coal crushing, grinding and sizing means;
(b) ground coal/water slurry preparation means;
(c) steam generating means; and (d) reactor means in which coal slurry is contacted with saturated steam.
12. The apparatus of Claim 11 including a first phase separation means.
13. The apparatus of Claim 12 including a second phase separation means for operation at a pressure lower than the first phase separation means.
14. The apparatus of Claim 11, 12 or 13 wherein the reactor operates in an ebullated bed mode, with saturated steam generated by the steam generating means acting as the fluidizing medium.
15. The apparatus of Claim 11, 12 or 13 wherein the steam generating means is a lignite-fired boiler, fed by lignite fines obtained from the coal crushing, grinding and sizing means.
16. The apparatus of Claim 13 including means for relieving the pressure between the first phase separation means and the second phase separation means.
17. The apparatus of Claim 11, 12 or 13 including heat exchange means for the recovery of process heat.
18. The apparatus of Claim 11, 12 or 13 including means for treating solid, liquid and gaseous effluent streams such that they are rendered suitable for recycle, the recovery of process heat, and environmentally acceptable disposal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000451992A CA1213844A (en) | 1984-04-13 | 1984-04-13 | Production of beneficiated lignite and brown coals |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000451992A CA1213844A (en) | 1984-04-13 | 1984-04-13 | Production of beneficiated lignite and brown coals |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1213844A true CA1213844A (en) | 1986-11-12 |
Family
ID=4127653
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000451992A Expired CA1213844A (en) | 1984-04-13 | 1984-04-13 | Production of beneficiated lignite and brown coals |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1213844A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8453953B2 (en) | 2005-04-29 | 2013-06-04 | Gtl Energy Holdings Pty Limited | Method to transform bulk material |
| US8673030B2 (en) | 2007-08-01 | 2014-03-18 | Gtl Energy Holdings Pty Limited | Methods of producing water-resistant solid fuels |
-
1984
- 1984-04-13 CA CA000451992A patent/CA1213844A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8453953B2 (en) | 2005-04-29 | 2013-06-04 | Gtl Energy Holdings Pty Limited | Method to transform bulk material |
| US8673030B2 (en) | 2007-08-01 | 2014-03-18 | Gtl Energy Holdings Pty Limited | Methods of producing water-resistant solid fuels |
| US9499756B2 (en) | 2007-08-01 | 2016-11-22 | Gtl Energy Holdings Pty Limited | Roll press |
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