MXPA00001788A - Heating with steam - Google Patents

Abstract

A method and an apparatus for heating a solid material in a process vessel are disclosed. The method includes the steps of:(a) supplying a charge of the solid material to the vessel to form a packed bed;(b) supplying a fluid to the packed bed to pressurise the contents of the vessel;(c) supplying steam to the vessel to heat the solid material in the packed bed by indirect heat exchange while maintaining the contents of the vessel under pressure;and (d) controlling the operating conditions in step (c). The operating conditions in step (c) are controlled to transfer heat to the solid material and allow water in the solid material to be removed as a liquid phase in a first"wet"stage of the method and to transfer heat to the solid material to boil at least a part of the remaining water from the solid material as a vapour phase in a second"dry"stage of the method.

Description

HEATING WITH STEAM The present invention relates to the process of loading a solid material to heat the solid material. The present invention specifically, but not exclusively, concerns the processing of a charge of solid material having low thermal conductivity under conditions including high temperature and pressure. The present invention relates more specifically to: i) the benefit of carbonaceous materials, usually coal, under conditions that include high temperature and pressure to increase the BTU value of carbonaceous materials by removing water from carbonaceous materials; and ii) cooling the heated carbonaceous materials.

U.S. Patent 5,290,523 to Koppel still describes a process for benefiting carbon by simultaneous application of pressure and temperature. Koppel an describes thermal dehydration of coal by heating coal under conditions that include elevated temperature and pressure to make the physical changes in the coal that give rise to the water removed from the coal by a "compression" reaction. Koppelman also indicates maintaining high enough pressure during the breeding process so that by-product water is produced mainly as liquid water rather than as steam. Koppelman also describes a range of different options in the apparatus to perform the prayer process. In general terms, the options are based on the use of a pressure vessel that includes an inverted conical inlet, a cylindrical body, a conical discharge and a unit of heat exchanger tubes placed in a vertical or horizontal direction, located in the body. In a proposal for the use of a Koppelman type apparatus, the tubes located in the vertical direction and the discharge end are packed with carbon, and nitrogen is injected to pressurize the tubes and the discharge end in advance. The coal is heated by indirect heat exchange with oil which is supplied as a heat transfer fluid to the cylindrical body externally of the tubes. In addition, the heating of the coal is favored by direct heat exchange between the coal and steam that acts as a working fluid inside the packed bed. In addition, the steam pressurizes the tubes and the discharge end to a necessary pressure. The combination of the elevated pressure and temperature conditions in the pipes and the discharge end evaporates some of the water from the coal and then condenses some of the water as liquid. A portion of the steam generated after the addition of water is also condensed as liquid in the colder regions of the tubes due to the high pressure. Steam that does not condense, and that is in excess of the requirements for optimal pressurization of the packed bed, must be ventilated. In addition, non-condensable gases (for example, CO, CO2) are released and it is necessary to ventilate them. The liquid is drained periodically from the discharge end. Finally, after a prescribed period of residence, the container is depressurized and the improved charcoal is discharged at the discharge end and subsequently cooled. The above-described proposal to use the Koppelman type apparatus requires the use of oil as a heat transfer fluid close to its operating temperature limit. This is not desirable from the environmental and occupational health point of view. Other high temperature liquids such as molten salt or molten metal can be used as alternatives but these also have limitations with use. In another proposal for use of a Koppelman type apparatus, steam is used instead of oil as a heat transfer fluid in direct rather than indirect contact with the coal. The disadvantages of this proposal include limited options to scale to a commercial plant size and difficulties in controlling the heating rate. An object of the present invention is to provide an improved method and apparatus for benefiting carbon by the simultaneous application of temperature and pressure which do not depend on the use of oil as the fluid for heat transfer. According to the present invention there is provided a method of heating a solid material in a process vessel, which method consists in: (a) supplying a load of solid material to the vessel to form a packed bed; (b) supplying a fluid to the packed bed to pressurize the contents of the container; (c) supplying steam to the container to heat the solid material in the packed bed by indirect heat exchange while maintaining the contents of the pressure vessel; and d) controlling the operating conditions in step (c): (i) transferring heat to the solid material and allowing the water in the solid material to be removed as a liquid phase in a first "wet" stage of the method; and (ii) transferring heat to the solid material to boil at least some of the remaining water of the solid material as a vapor phase in a second "dry" stage of the method. The term "operating conditions" is understood as the conditions that a carrier has with the heating of the solid material and the removal of water from the solid material and includes, for example, the operating conditions such as vapor pressure, vapor temperature and flow rate. of the vapor that influence the temperature in the packed bed. It is preferred that step (d) is to control the operating conditions so that a substantial portion of the vapor condenses during the indirect heat exchange with the solid material in the packed bed in the wet phase of the method. It is particularly preferable that step (d) is to control the operating conditions so that at least 80% of the vapor condenses during the indirect heat exchange with the solid material in the packed bed in the wet phase of the method. It is preferable that the wet stage of the method heat the solid material to a t? perature in the order of 250 ° C. It is preferred that the dry stage of the method include: (i) a "drying" part during which the rest of the water that is removed in the dry stage boils off the solid material; and (ii) a subsequent heating part during which the solid material heats to a final temperature. It is preferred that the final temperature of the solid material in the dry stage be on average in the range of 270 ° C to 420 ° C to ensure the optimum benefit of the solid material. To achieve temperatures of at least 270 ° C in the dry stage, it is preferred that the method consist of supplying superheated steam during the dry stage of the method. It is particularly preferred that step (d) is to control the operating conditions so that the pressure of the superheated steam in the dry stage of the method is greater than the pressure in the packed bed to promote boiling of the water in the packed bed. Typically, step (d) consists of controlling the vapor pressure in the wet stage relative to the pressure in the packed bed to control the condensation temperature of the vapor that is lower than the boiling temperature of the water in the bed packed. This step guarantees the operation that avoids the boiling of the water exuded from the solid material in the packed bed during the wet stage of the method. It is preferred that the method consist of: (a) supplying superheated steam to a first process vessel for heating the solid material in the bed packed in the first vessel by indirect heat exchange during the dry stage of the method; (b) supplying the vapor discharged from the first process vessel to a second process vessel for heating the solid material in the bed packed in the second vessel by indirect heat exchange during the wet process step. The above described use of two (or more) process vessels with separate charges of the solid material is particularly advantageous because steam is used in a superheated state in the dry stage to heat the solid material in the packed bed at temperatures to boil the water of the solid material and further heating the solid material to a final temperature and then using steam in the wet stage to heat the solid material without boiling the water in the solid material. It is particularly preferred that the method further consist of: (a) discharging the heated solid material from the first rori 'or op f or Ha onii? HO rnm? l of a 1 a? d-a a a hiraorj a seca of the method and eliminate a necessary level of water from the solid material during these stages; (b) filling the first container with solid material and pressurizing the contents of the container; and (c) changing the steam flow so that the superheated steam flows first through the second vessel to heat the solid material in the packed bed by indirect heat exchange in the dry method stage and the steam discharged from the second vessel flows through the first container and heat the solid material in this vessel by indirect heat exchange in the wet stage of the method. It is more particularly preferred that the method consist of repeating the sequence described above of the steps of emptying and filling the containers and changing the flow of vapor through the containers. In accordance with the present invention there is also provided an apparatus for heating a. solid material comprising: (a) a process vessel for containing a packed bed of the solid material; and (b) a heat exchanger circuit for supplying steam to the process vessel for heating the solid material in the packed bed by indirect heat exchange, whose heat exchange circuit comprises: (i) a heat exchange unit in the process vessel, the unit consisting of a passage for steam and a plurality of heat exchange surfaces which, in use, extend to the packed bed; (ii) a condenser for condensing steam discharged from the heat exchange unit; and (iii) a heater or boiler for heating steam for the heat exchange unit of condensed water in the condenser. It is preferred that the exchange circuit further comprises a means for storing steam to allow variations in flow and pressure during normal operating conditions, loading / unloading, starting and stopping.

It is preferred that the apparatus contain two or more process vessels for containing packed beds of the solid material. With this arrangement, it is preferred that the heat exchanger circuit comprises one of the heat exchange units in each of the containers and that the heat exchange units are connected to each other so that the steam can flow in series or in parallel through the heat exchange units. The present invention is further described by the example with reference to the accompanying drawings, of which: Figure 1 illustrates as a schematic a preferred embodiment of the method and apparatus of the present invention for heating a solid material; Figure 2 illustrates as a schematic another preferred embodiment of the method and apparatus of the present invention for heating a solid material; and Figure 3 illustrates as a schematic another preferred embodiment of the method and apparatus of the present invention for heating a solid material. The following description is in the context of heating coal to benefit coal by separating water from coal to increase its calorific value. The present invention is not limited to this application and extends to the processing of any suitable solid material. The method and apparatus illustrated in Figure 1 is based on the use of a single pressure vessel 65 that is constructed to receive and retain a packed coal bed under the conditions of elevated temperature and pressure. The process vessel can be any suitable type of pressure vessel, such as that described in International application PCT / AU98 / 00005 entitled "A reactor", PCT / AU98 / QQ142 entitled "Process vessel and method of treatment of a material charge ", PCT / AU98 / 0Q204 entitled" Liquid / gas / solid separation, and PCT / AU98 / 00324 entitled "Enhanced heat transfer" in the name of the applicant The description of these international applications is incorporated herein by reference .

The apparatus further consists of a heat exchanger circuit for supplying steam to the vessel 65 to heat the coal by indirect heat exchange. The heat exchanger circuit consists of: (i) a unit of heat exchanger plates located in the vertical direction, generally identified by the number 64, which defines surfaces? ~, For heat transfer and includes passages (not shown) for the steam; (ii) a condenser 62 connected to the discharge end of the heat exchange unit 64 to condense any vapor that is not condensed; (üi) a heating unit 60 connected to the condenser 62 to generate steam for the heat exchange unit 64. The heat exchanger circuit further comprises a steam accumulator 61 at the intake end of the heat exchange unit 64 which stores steam and ensures controlled pressure in the conduits of the unit 64 and a valve for the pressure control 66 at the discharge end of the heat exchange unit 64. The apparatus illustrated in Figure 1 further comprises a circuit, generally identified by the number 71, to circulate a working fluid through the packed coal bed 67 to improve the heat exchange between the steam flowing through the heat exchanger unit 64 and the coal in the packed coal bed 67. The fluid Preferred work is a gas that does not undergo a phase change under the operating conditions of the method. The gases that can be used as working gas include nitrogen, steam, SO2, CO2, hydrocarbons, noble gases, refrigerants and mixtures thereof. The apparatus illustrated in Figure 1 further comprises an inlet 77 for introducing a gas into the container 65 to pressurize the container 65. During the use of the apparatus illustrated in Figure 1 according to a preferred embodiment of the method of the present invention: ) the coal is supplied to the vessel 65 to form a packed coal bed 67; ii) the contents of the container 65 is pressurized with a gas supplied from outside, steam generated internally or both at a required pressure; (iii) the steam is supplied to the heat exchanger unit 64 to heat the coal in the packed coal bed 67. The combined effect of pressure and temperature in the container 65 removes the water from the coal. The steam is supplied to the heat exchanger circuit 64 from the heater unit 60 at a temperature of at least 300 ° C. It will be noted that the importance of avoiding devolatilization of coal is a factor that determines the upper limit of the temperature of the steam. It should also be noted that with other solid materials the maximum steam temperature can be limited only by the heater and not by the solid materials. The accumulator 61 controls the supply of steam to the heat exchanger unit 64 to provide a reasonably constant condensing speed in the condenser 62. The pressure control valve 63 is used to control the pressure in the heat exchanger unit 64 and by both control the condensation temperature. The parameters required for the pressure control valve 63 will depend on the heat transfer on the side of the carbon bed in the container 65. In the preferred embodiment of the method of the present invention, the operating conditions are. controlled to remove water from coal in two stages, with: (i) the water being "squeezed out" of the coal and drained as a liquid phase to a lower section of the vessel 65 in a wet first stage of the method; and (ii) a substantial part of the water remaining in the coal being separated as a vapor phase in a second dry stage of the method. In the preferred embodiment of the method of the present invention the removal of the two-stage water from the coal in the packed bed 67 is advantageously obtained by using steam in the wet stage of the method and superheated steam in the dry stage of the method. The wet phase of the method can be operated efficiently with saturated steam and allows a substantial proportion (usually 80%) of the steam to be condensed. However, steam will usually not heat the coal in the packed bed at temperatures greater than 270 ° C, which are necessary in the dry phase of the method to boil a substantial part of the water remaining in the coal after completing the wet phase of the method. Usually, the dry phase requires final temperatures of the coal above the steam line and therefore the saturated steam will not reach these temperatures. It will be noted that the superheat temperature of the vapor must be maintained within the limits at which the carbon can be exposed without significant devolatilization. This imposes limits on the equilibrium of the available heat in the wet and dry stage. In the heating of materials i? solids without limiting the maximum temperature, there is more opportunity to optimize the use of energy in the steam. The applicant has found that it is preferable to: (i) operate the dry stage of the vapor pressure method greater than the pressure found in the packed coal bed 67 to promote the boiling of the water in the coal by condensation of the steam in the supply side or use superheated steam at any pressure; and (ii) operating the wet process step at a lower vapor pressure than in the packed coal bed 67 to maintain the condensing temperature of the vapor below the boiling temperature of the water in the packed coal bed 67. A characteristic of the above-described control of the vapor pressure to be greater than the pressure on the side of the bed in the dry stage of the method is that, when coupled with a working fluid the flow of the mass through the circuit 71 there is a high heat transfer not only for coal particles but also for any water in the packed coal bed 67. This is a particularly important feature in the case where the bed is not wet and heat transfer between solids and liquids it is low. The preferred embodiment of the present invention also comprises the use of reverse fluid of the working fluid in an asymmetric configuration during the wet stage of the method with larger pulses in a downward direction compared to an upward direction to drive the water in the liquid phase down towards the lower end of the container 65. This asymmetric working fluid flow can accelerate the drainage of water from the packed coal bed 67. The applicant has found that in the specific example the amount of heat needed in the dry phase and the The amount of heat required in the wet phase is approximately in proportion to the available one single flow of superheated steam mass, and this finding contributes to a greater efficiency of steam condensation when the invention is used. If more steam is required in the dry phase, the efficiency of the condensation is reduced unless it can be adequately restored with a higher degree of super heat. If lower amounts of steam are required in the dry phase then the superheated steam is diverted to the saturation stage, and an efficiency close to 100% must be achieved. The method and apparatus illustrated in Figure 2 is an extension of the arrangement illustrated in Figure 1 and is based on the use of two pressure vessels 56a, 56b. The apparatus also comprises two groups of flow control valves. A first group of valves Ll, L3, R4 and R2 operate together and a second group of control valves Rl, R.3, L4 and L2 operate together, but in phase opposite to the first group of valves. Thus, when the first group of valves is open, the second group of valves is closed. It can be easily appreciated that the change of state of each valve group reverses the sequence of steam flow through the vessels 65a, 65b. During the use of the apparatus illustrated in Figure 2, according to the preferred embodiment of the method of the present invention, after reaching the operation in the steady state, the containers 65a, 65b are successively filled with carbon, the vessels 65a, 65b are pressurized and coal is heated in the preferred two-stage method by indirect heat exchange with steam, and containers 65a, 65b are emptied after completing the second dry stage of the method. Specifically, the steam flow successively changes through the vessels 65a, 65b so that: (i) first, the superheated steam flows through the vessel 65a and heats the coal in the dry method and steam stage ( which is no longer superheated) discharged from the first container 65a flows through the second container 65b and heats the carbon in the wet process step; and (ii) secondly, the superheated steam flows in the alternate route through the vessel 65b and heats the coal in the dry method step and the steam discharged from the second vessel 65b flows through the vessel 65a and heats the coal in the wet stage of the method. The sequence of steps described above involves filling and emptying each container 65a, 65b and, as a consequence, there will be downtimes in the cycle of each container. Furthermore, in a preferred mode of operation, the first and second valve groups are opened during a permutation when a container 65a, 65b is being emptied and filled and, thereafter, the necessary group of valves is progressively closed to avoid pressure waves in the system. The method and apparatus illustrated in Figure 3 is an alternative arrangement for that shown in Figure 2. With reference to Figure 3, the apparatus consists of 6 process vessels 65a, b, c, d, e, f (only one of which is shown in the figure) containing packed coal beds and a heat exchanger circuit for 1Q supply the saturated steam and superheated steam to the containers to heat the coal by indirect heat exchange in the wet and dry stages. Described above in relation to Figures 1 and 2. There are some similarities and differences between the heat exchanger circuit shown in Figure 3 and that shown in Figures 1 and 2. One similarity is that the heat exchanger circuit it includes the unit of vertically placed heat exchanger plates 64, the boiler 60 and the condenser 62. One difference is that the heat exchanger circuit includes a superheated steam collector 91 and a saturated steam collector 93 for storing the superheated and saturated steam , upstream of the containers. The manifolds 91, 93 are provided to allow variations in flow and pressure in the heat exchange units 64 in the containers. A second difference is that, the heat exchanger circuit includes a series of tubes and valves to allow separate supply of saturated steam through the manifold 93 (line 81, valve V) and superheated steam through the manifold 91 (line 83, valve V2 ) to each of the containers 65a, b, c, d, e, f to heat the coal under high pressure in the wet and dry stages as already described. In addition, the heat exchanger circuit includes: (i) a water / steam separator 95 at the discharge end of the heat exchange unit 64 of each container to separate the steam and water discharged from the heat exchange units 64; and (ii) the pipe 101 for transferring separate water to the pipe for the purpose of forcing separate steam to the saturated steam collector 93. It is possible to make multiple modifications to the preferred embodiment described above without departing from the spirit and Scope of the present invention For example, it is within the scope of the present invention to combine the invention with power ratio as described in the Australian preliminary application, applicant's filing filed on the same date as the present Australian provisional application. The description in this other Australian provisional application is incorporated herein by reference.

Claims (18)

91 CLAIMS

1. A method of heating a solid material in a process vessel, which method comprises: (a) supplying a load of solid material to the vessel to form a packed bed; (b) supplying a fluid to the packed bed to pressurize the contents of the container, (c) supplying steam to the container to heat the solid material in the packed bed by indirect heat exchange while maintaining the contents of the pressure vessel; and d) controlling the operating conditions in step (c): (i) transferring heat to the solid material and allowing the water in the solid material to be separated as a liquid phase in a first "wet" stage of the method; and (ii) transferring heat to the solid material to boil at least some of the remaining water of the solid material as a vapor phase in a second "dry" stage of the method.

The method defined in claim 1, wherein step (d) further comprises controlling the operating conditions so that a substantial portion of the vapor condenses during indirect heat exchange with the solid material in the packed bed in the phase Wet of the method.

3. The method as defined in claim 2, wherein step (d) further comprises controlling the operating conditions so that at least 80% of the vapor condenses during the indirect heat exchange with the solid material in the packed bed in the Wet phase of the method.

4. The method defined in any of the preceding claims, wherein the wet process step heats the solid material at a temperature up to 250 ° C. The method defined in any of the preceding claims, wherein the dry stage of the method includes: (i) a "drying" part during which the remaining water that separates in the dry stage boils from the solid material; and (ii) a subsequent heating part during which the solid material heats to a final temperature. The method as defined in claim 5, wherein the final temperature of the solid material in the dry stage is on the average in the range of 270 ° to 420 ° C to ensure the optimum benefit of the solid material. 7. The method defined in any of the preceding claims comprises supplying superheated steam during the dry stage of the method. The method defined in claim 7, wherein step (d) comprises controlling the operating conditions such that the pressure of the superheated steam in the dry stage of the method is greater than the pressure in the packed bed to promote boiling of the water in the packed bed. The method defined in any of the preceding claims 7, wherein step (d) comprises controlling the vapor pressure in the wet dry stage in relation to the pressure in the packed bed to control the condensation temperature of the vapor that is less than the boiling temperature of the water in the packed bed. The method defined in any of the preceding claims comprises: (a) supplying superheated steam to a first process vessel for heating the solid material in the bed packed in the first vessel by indirect heat exchange during the dry stage of the method; (b) supplying the vapor discharged from the first process vessel to a second process vessel for heating the solid material in the bed packed in the second vessel by indirect heat exchange during the wet process step. 11. The method defined in claim 10 further comprises: (a) discharging the heated solid material from the first container after completing the wet and dry steps of the method and separating removing a required level of water from the solid material during these steps; (b) fill the first container with solid material and pressurize the content of the recipient * r (c) change the steam flow so that the superheated steam first flows through the second vessel to heat the solid material in the packed bed by indirect heat exchange in the dry method stage and the vapor discharged from the second vessel flows through the first vessel and heats the solid material in This vessel by indirect heat exchange in the wet stage of the method. 12. The method defined in claim 11 comprises repeating the sequence of steps of emptying and filling the containers and changing the flow of vapor through the containers. 13. an apparatus for heating a solid material, which consists of: (a) a process vessel to contain a packed bed of solid material; and (b) a heat exchanger circuit for supplying steam to the process vessel for heating the solid material in the packed bed by indirect heat exchange whose heat exchanger circuit comprises: (i) a heat exchanger unit in the vessel of the heat exchanger. process, whose unit comprises a passage for steam and a plurality of heat exchange surfaces which, in use, extend towards the packed bed; (ii) a condenser for condensing steam discharged from the heat exchanger unit; and (iii) a boiler to generate steam for the heat exchanger unit from the condensed water in the condenser. The apparatus defined in claim 12, wherein the exchanger circuit further comprises a means for storing steam to allow variations in flow and pressure during normal operating conditions, charging / discharging, starting and stopping. 15. The apparatus defined in claim 13 or 14 further comprises two or more process vessels for containing packed beds of the solid material. The apparatus defined in claim 13, wherein the heat exchanger circuit comprises one of the heat exchange units in each of the containers and the heat exchange units are connected to each other so that the steam can flow in series or in parallel through the heat exchange units. 17. A method of heating the solid material in a process vessel substantially as described above with reference to the accompanying drawings. 18. An apparatus for heating a solid material substantially as described in the foregoing with reference to the accompanying drawings.