BACKGROUND OF THE INVENTION

1. Field of the Invention This invention relates to an apparatus and method for preparing coal for safe shipment and transport. More particularly, the invention relates to a rotary cooler used in a coal processing facility wherein process derived fuels (PDF) or coal char is simultaneously rehydrated and cooled to produce a solid fuel that can be stored and transported without posing potentially serious combustion hazards due to self-heating.

2. Description of Related An

The most abundant coal resources in western North America are low rank coals, including sub-bituminous and lignite. Many deposits of these coals are relatively inexpensive to mine compared to higher-rank coals in eastern North America, Australia, Indonesia, and Europe, but their economic value is reduced because they contain large amounts of moisture and oxygen in combined form. The significant amount of moisture contained within the mined coal results in both increased transportation costs from the coal deposit to the point of use, and decreased heat available from the coal when burned, because of the heat required to evaporate the moisture content. The problem exists in subbituminous coals and is particularly acute with low-rank coals which may contain from 10% to 50% moisture when mined.

A well-known practice to reduce the moisture content in coal is to dry it by heating the coal at 80°-150 ^β C. The drying method, however, has a disadvantage because the resultant PDF tends to readily reabsorb moisture from the atmosphere and to approach its previous moisture content state. Drying methods are also used in producing process derived fuel whereby dried coal char is obtained using a pyrolytic process. Drying coals can lead to a more serious problem relating to the propensity of PDF to "self-heat."

Self-heating, also referred to as "autogenous" heating or pyrophoricity, is the tendency of a material to spontaneously heat at ambient conditions. It is well known that PDF has a propensity to self-heat when stored and shipped at warm and moist ambient conditions. When exposed to the atmosphere, PDF will rapidly adsorb both moisture and oxygen and subsequently heat up until it ignites. Commonly referred to as "spontaneous combustion," self-heating of coal presents a serious hazard whenever substantial amounts of PDF are stockpiled or transported.

A first major cause of self-heating of PDF results from oxidation of the coal at ambient conditions which results in an exothermic reaction. Oxygen physically adsorbs onto the surface of the PDF and chemically reacts with organic molecules within the PDF. During this reaction, organically-bound carbon is converted into carbon dioxide with an ultimate heat release of approximately 400 kJ per mole. Because oxidation rates will approximate¬ ly double with each 10" C rise in temperature, these heat releases, if not quickly dissipated, will promote a self-accelerating oxidation process and cause the coal to heat up progressively more quickly toward an ignition temperature.

A second major cause of self-heating occurs when dried coal adsorbs water, either in liquid or vapor form. At ambient temperatures, carbon oxidation rates are generally too small to initiate the oxidation of dried coal. However, when dried coal is wetted by water, heat is released due to the adsorption of water onto the dried coal. Such "heat of wetting" will raise the temperature of the coal to levels at which carbon oxidation can occur more rapidly. The increased oxidation rates can eventually lead to spontaneous combustion. This mechanism explains why spontaneous combustion of coal commonly occurs after rain following a period of dry hot weather. This mechanism also takes effect when dry coal is placed on wet ground and when wet coal is loaded onto an established, partially dried-out stockpile. In the latter cases, heating invariably begins at the interface between wet and dry material. If the wetting of coal is non-uniform, i.e., results in coal having variations with less than equilibrium moisture content, self-heating random hot spots may be produced in the coal. The random hot spots can cause spontaneous

combustion of the coal during storage or transport. Therefore, it is very important to uniformly rehydrate or wet the coal to produce coal having an equilibrium moisture content. Therefore, there is a need for a method to produce PDF in such a manner as to reduce or eliminate the propensity for self-heating.

There have been many attempts at processing coal char to produce a process derived fuel which is safe to transport and store. For example, U.S. Pat. No. 3,961,914, Kiπdig et al. disclosed coating dried coal particles with a silicon dioxide film. Johnson et al., in U.S. Pat. No. 3,985,516 disclosed the coating of sub-bituminous and lignite coal particles with heavy liquid hydrocarbon (for example, crude oil residuum) in a fluidized bed after drying. Both of these prior art processes suffer disadvantages related to the foreign inert fluids used to coat the coal. Coal coatings of inert fluids not only introduce additional costs into the coal processing facility, they also reduce the fuel efficiency of the coal. Because these processes require a large amount of inert fluids, it is almost impossible to spread the fluids uniformly upon the surface of coal lumps. In addition, the fluids tend to ooze out of the coal during transportation and storage, which adds to storage and handling costs.

In U.S. Pat. No. 4,192,650, Seitzer disclosed the prevention of autogenous heating by rehydrating dried coal with steam at 100" C to 115" C to yield a moisture content of 2% to 10%. Berkowitz, in U.S. Patent No. 4,586,935, described a method of treating low-rank coals which included heating the coal by immersion in molten metal to a temperature not much higher than 30" C to 50" C above its decomposition temperature and then quickly cooling it to room temperature by quenching it in water or other suitable medium. The heating process causes pyrolytic material to diffuse from the interior to the surface of the coal particles. The quenching process causes the pyrolytic material to plug the pores of the coal which prevents moisture reabsorption and oxygen adsorption. One disadvantage of this process is the need for exposing the coal to a molten metal bath prior to quenching. Not only does the molten metal bath introduce added complexity and expense to the treatment facility, but it is difficult to precisely

maintain the temperature of the bath at the desired temperature. A second disadvantage of this process is that the coal is not uniformly treated by the water resulting in uneven plugging of the coal pores. Partially wetted coal char is prone to self-heating while stored. In addition, this process does not account for the significant amount of heat produced when the coal is quenched with water, which adds to the cooling time.

Ito et al., in U.S. Patent No. 4,769,042, describe a process for the heat treatment of coal which comprises heating and drying low grade coal with a high temperature gas in a fluidized bed and subsequently cooling the coal by applying a cooling gas of high steam content in a first cooling step, followed by spraying the coal with water until it holds the maximum moisture possible. This process is impractical because it cannot be used in existing coal processing facilities using a pyrolytic chamber and furnace, whereby the processing temperatures can reach approximately 900° C. The fluidized bed required by this process adds costs and complexity to existing coal processing facilities. The wetting performed in this process suffers the disadvantage of momentary water-to-coal contact time, inadequate water-to-coal exposure, and very little stirring of the processed coal.

Moreover, the Ito process does not provide a cooling mechanism to account for the tremendous heat created when dry hot coal char is wetted. The Ito cooling process is potentially self-limited because the heat produced when the coal is wetted increases the coal temperature by approximately 300" F, which in turn causes the water used for wetting to evaporate and thus limit cooling. Because water adsorption is a reversible process (that is, because the water used for wetting and cooling can evaporate as the wetted char is heated) hot spots can occur on the coal surface which can lead to self- heating. Therefore, there is a need for a coal treatment process which limits or elimi¬ nates PDF self-heating, yet reduces the heat caused by wetting. There is a need for such a coal treatment process which is inexpensive and simple to implement and reduces coal treatment processing times by removing the heat caused when PDF is wetted.

The prior art means for rehydration of coal char was often characterized by momentary contact time between coolant water and processed coal char. For example, one prior art system used an air atomized water spray to spray water upon a moving char stream as the char entered a storage silo. One disadvantage of this system was due to the erratic regulation of water flow to the solid coal char stream. Erratic regulation of water flow was due to the fact that the water nozzles of the water spray often became plugged with coal debris. However, even when the water flow was properly regulated, the char stream flow rate often became erratic. As a result, the prior art rehydration means was characterized by intermittent and momentary water-to-coal contact times, inadequate application of water to coal char surface area, and no means for mixing the coal char to increase the coal char surface area exposed to water. Contacting the moving coal char stream with water as it passed in front of the water spray nozzles resulted in non-uniform application of water to the coal char. The partially wetted coal char was known to self- heat during storage in the storage silo. Therefore, there is a need for a rehydration mechanism which increases water-to-coal contact times, uniformly applies water to coal char surface area, and mixes the coal char stream to maximize the coal char surface area exposed to water spray.

The present invention provides such a coal treatment process.

SUMMARY OF THE INVENTION

The present invention provides an improved coal rehydration cooler having a means for transporting coal char though the cooler, a means for uniformly rehydrating or wetting the coal char as it is transported through the cooler, and a cooling means for compensat- iπg for the heat produced when the coal char is rehydrated. In the preferred embodi¬ ment, the rotary cooler is inclined so that coal char is biased by the force of gravity to move from an inlet end of the cooler to an outlet end. Alternative embodiments use other transport means, such as used in trough-and-screw type mixers.

In one preferred embodiment, the rotary cooler has a plurality of coal char lifters which are spaced apart and affixed to the walls of the cooler in a position proximate a water spray apparatus. As coal char is transported through the cooler, it is raised by the lifters into a position in front of the water spray apparatus where it is sprayed with rehydration water.

In the preferred embodiment of the present rotary cooler, a plurality of heat exchanger tubes are affixed to the walls of the cooler. The heat exchanger tubes carry fresh cooling fluid throughout the length of the cooler. As the cooler rotates, the heat exchanger tubes contact the coal char and thereby gently mix and cool the coal char. As the coal char travels the length of the cooler, it is slowly mixed by the heat exchanger tubes and the lifters, and is rehydrated by the water sprayed from the water spray apparatus. The heat of wetting produced by the rehydration process is removed by the heat exchanger tubes.

An alternative embodiment of the present rotary cooler uses several stages of rehydration. In this alternative embodiment, the coal char is rehydrated by a plurality of water spray apparatuses positioned along the centeriine of the rotary cooler. Each water spray apparatus has a plurality of lifters positioned proximate the apparatus which lift the coal char for rehydration. In order to assure that the coal char is uniformly rehydrated within

the cooler, the present invention has a plant control system which regulates the rehydration water flow rate, the coal char feed rate, and the coal char flow rate.

The plant control system monitors and controls the operation of the rehydration rotary cooler. By monitoring the temperatures of the coal char and the exchanger tubes cooling fluid (at entrance and exit of the cooler), the plant control system calculates the optimum cooling fluid, rehydration water, and coal char flow rates. The plant control system uses closed-loop control systems to control these flow rates in order to optimize the rehydration process.

The rotary cooler may optionally use either reclaimed or "oily" water supplies for rehydration. Reclaimed rehydration water from other process sources can become dirty or oily after several uses, and can cause the prior art water sprays to become clogged with coal debris. One solution to the clogging problem taught by the present invention is the use of filter systems to filter out coal debris from the rehydration water supply.

Another solution to the water spray problem is to alternatively use an improved water spray referred to as an oscillating water distributor. The oscillating water distributor uses a serrated twin weir rotating trough evenly distributes water to the coal char bed without the use of a water spray nozzle. The trough width and height are varied along the circumference of the distributor. The design of the distributor eliminates clogging associated with nozzles. As the distributor rotates, it forces coal debris out of the trough and into the cooler char bed.

The details of the preferred embodiment of the present invention are set forth in the accompanying drawings and the description below. Once the details of the invention are known, numerous additional innovations and changes will become obvious to one skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a side cross-sectional view of the preferred embodiment of the energy compensated coal rehydration cooler of the present invention.

FIGURE 2 is a side cross-sectional view of an alternative embodiment of the energy compensated coal rehydration cooler of the present invention, equipped with a multi-stage water spray arrangement.

FIGURE 3 is a schematic diagram of a control system for the energy compensated coal rehydration cooler of FIGURES 1 and 2.

FIGURE 4a is side view of an oscillating wetting distributor used in an alternative embodiment of the water spray apparatus used in the energy compensated coal rehydration cooler shown in FIGURES 1 and 2.

FIGURE 4b is a cross-sectional view of the oscillating wetting distributor shown in FIGURE 4a taken along lines B-B.

FIGURE 4c is a cross-sectional view of the serrated twin weir trough of the oscillating wetting distributor shown in FIGURE 4b taken along lines A-A.

FIGURE 4d is a cutaway front perspective view of the oscillating wetting distributor shown in FIGURES 4a-4c.

Like reference numbers and designations in the various drawings refer to like elements.

DETAILED DESCRIPΗON OF THE INVENTION

Throughout this description, the preferred embodiment and examples shown should be considered as exemplars, rather than as limitations on the present invention.

FIGURE 1 shows the rotary cooler of the present invention equipped with a single stage rehydration arrangement. The cooler is shown having a generally cylindrical configura¬ tion, although other configurations may be used in alternative embodiments. In the preferred embodiment shown in FIGURE 1, the rotary cooler is of conventional design, with the exception of the improvements provided by the present invention. An example of the rotary cooler used to practice the present invention is the "Rennenburg" rotary cooler available from the Rennenburg division of Heyl & Patterson, Inc., located in

Pittsburg, Pa. The preferred Rennenburg rotary cooler used to practice the present invention is approximately 50 feet long, has a diameter of approximately 11 feet, and has a capacity of approximately 3.8 Million BTU/hr.

As shown in FIGURE 1, the rotary cooler 100 of the present invention is a generally cylindrical vessel having a plurality of heat exchanger tubes 102 affixed to the walls 104 thereof. The heat exchanger tubes provide a mechanism for cooling the rotary cooler 100 to a desired internal temperature. The heat exchanger tubes 102 preferably extend the length of the cooler 100 and are preferably comprised of abrasive resistant material such as stainless steel. The heat exchanger tubes 102 transport cooling fluid throughout the rotary cooler 100. Preferably the cooling fluid comprises cooled water, however, other cooling fluids may be used. Fresh cooling fluid enters the rotary cooler at an inlet (FIGURE 3) in the exchanger tubes 102 while heated cooling fluid exits the exchanger tubes at an outlet (FIGURE 3). The cooling fluid flow rate is controlled by a fluid valve and described in more detail below with reference to FIGURE 3.

Coal char or PDF enters the rotary cooler 100 through an inlet 106 and exits the rotary cooler 100 through an outlet 108 after rehydration. The size and shape of the inlet 106

and outlet 108 can vary, but they are preferably sufficiently large to permit coal char to flow through the cooler 100 at a desired rate. As shown in FIGURE 1, the cooler 100 has a char dam 110 which helps regulate the flow of char out of the cooler 100. The control of the PDF flow rate is described in more detail below with reference to FIGURE 3. The embodiment of the rotary cooler 100 shown in FIGURE 1 has a water spray apparatus 112 which has a nozzle 113 preferably facing toward the inlet 106. The water spray nozzle 113 is well known in the art and is commercially available from a number of manufacturers. For example, one commercially available nozzle is the WhirlJet ^® and FullJet* nozzles (type AASSTC, type 104, and type G) available from Spraying Systems, Inc., located in Wheaton, Illinois. The water spray apparatus 112 is positioned within the cooler 100 to ensure that, during use, water is sprayed substantially along a centeriine or center of gravity 114 of the rotary cooler 100.

Water is supplied to the water spray apparatus through a water supply line 116 which enters the rotary cooler through a rotary union 118. As shown in FIGURE 1, the water supply line 116 is positioned proximate the centeriine 114 of the cooler 100 and is supported by at least one support bracket 120. In the embodiment shown in FIGURE 1, the rotary cooler 100 has a plurality of coal char lifters 122 which are preferably equally spaced apart and affixed to the walls of the cooler 100 in a position proximate the water spray apparatus 112. The operation of the lifters 122 is described in more detail below.

In an alternative embodiment of the present invention, the water in the water supply line 116 is reclaimed from other processes and is subsequently used to rehydrate the coal char. Reclaimed rehydration water may become dirty or oily. The reclaimed water can be cleansed by using filters to filter out some of the coal debris. However, even when filters are used for the reclaimed water supply, the water can remain oily or dirty. Oily rehydration water tends to plug the nozzle 113 which hinders the rehydration process. The solution to this plugging problem is discussed in detail below with reference to FIGURES 3 and 4.

As shown in FIGURE 1, the rotary cooler 100 preferably is supported by a plurality of support tires 124. During use, the water spray apparatus 112, the water supply line 116, and the support bracket 120 rotate with the cooler 100 about the centeriine 114. The coal char which is present within the rotary cooler is lifted by the lifters 122 and sprayed by the water spray apparatus 112 during use. The operation of the present rotary cooler

100 is now described in more detail with reference to FIGURE 1.

Coal char 126 enters the rotary cooler 100 in an granular aggregate form at inlet 106. The present rotary cooler 100 is intended to be used in a coal processing system (not shown) which processes coal to maximize its caloric and commercial value. This process mildly pyrolyzes subbituminous coal to produce solid and liquid coal products. During this process, coal is dried and pyrolyzed by inertly heating the coal to temperatures exceeding 500° F. As a result of the pyrolytic process, coal loses its moisture and some of its volatile matter, forming coal char. After the coal is pyrolyzed, it is initially cooled to temperatures below 500" F. Therefore, the coal char aggregate 126 that enters the inlet 106 typically has a temperature of less than 500" F and a moisture content of less than

1% by weight. The rotary cooler 100 functions to both cool and rehydrate the heated and dried coal char.

The rotary cooler 100 is preferably inclined so that an inlet end 128 of the rotary cooler 100 is raised above an outlet end 130. Because the rotary cooler 100 is so inclined, gravity operates to bias the flow of coal char aggregate 126 toward the outlet end 128 of the rotary cooler 100. Additionally, the rotary cooler 100 preferably rotates at a selectab¬ le rate about its centeriine 114. The rate of rotation is controlled by a computerized Plant Control System (PCS) which is described in more detail below with reference to FIGURE 3. As the rotary cooler 100 rotates, aggregate coal char 126 is slowly transported along the length of the cooler from the inlet end 128 to the outlet end 130.

The coal char 126 makes contact with the surfaces of the heat exchanger tubes 102 as the heat exchanger tubes 102 rotate with the cooler 100.

In alternative embodiments, the coal char 126 can be transported within the cooler using alternative transport mechanisms such as trough-and-screw mixers. These mixers usually consist of single or twin rotors which continually turn the coal char as it progresses toward the discharge end. For example, one trough-and-screw mixer is a continuous hollow screw conveyor having multiple spray nozzles and a fluid cooled internal shaft.

Two or four screws may be used. One example of this type mixer is the Holo-Flite* Processor manufactured by the Denver Equipment Division of the Joy Manufacturing Company. Another alternative uses a "porcupine processor" which has an agitator to cut and fold the coal char as it is cooled. Breaker-bar assemblies, consisting of fingers extending toward the shaft, are frequently used to improve agitation. An example of this type of mixer is the Porcupine Processor available from the Bethlehem Corporation.

When the coal char 126 is transported into a position adjacent the lifters 122, it is slowly lifted into a position above the water spray apparatus 112. At this position, the coal char is forced by gravity to fall to the bottom of the cooler 100 through a position 132 substantially adjacent and proximate the water spray apparatus 112. As the coal char 126 passes through the position 132 it is sprayed by rehydration water. This process continues until the coal char is sufficiently rehydrated by the water. Due to the force of gravity and the rotation of the cooler 100, the coal char 126 is transported along the length of the cooler from the inlet end 128 toward the outlet end 130. As the coal char 126 is transported throughout the cooler 100, it is cooled by the heat exchanger tubes 102 which extend the length of the cooler 100. Cooled and rehydrated coal char exits the rotary cooler 100 at discharge outlet 108.

The time that coal char is present in the cooler 100 is referred to as coal char retention or residence time. The longer coal is resident within the cooler 100, the more the coal is exposed to the heat exchanger tubes 102, and the cooler the coal becomes. It is desirable to control the coal retention time to maximize coal cooling yet minimize rehydration processing time. In the preferred embodiment, the coal retention time ranges from 10 to 20 minutes. The char dam 110 helps to retain coal char within the rotary

cooler 100 and thus increase coal char retention time. Preferably, the coal char 126 has a uniform retention time (that is, all of the coal char is resident in the cooler for approximately the same period of time). Under conditions requiring uniform retention time, coal char must be fed into the cooler 100 in the correct ratio with respect to the rate that the rehydration water is fed into the cooler 100. The plant control system regulates the coal char feed rate and the rehydration water feed rate appropriately. The rate that coal char flows through the length of the cooler 100 is also controlled by the PCS. The PCS is described in more detail below with reference to FIGURE 3.

In addition to optimizing the coal char retention time, the present cooler 100 also increases the water-to-coal contact time as compared to the contact times provided by prior art rehydration systems. The velocity of coal char 126 flow through the rotary cooler 100 is reduced from prior art flow rates of 90 feet per minute to approximately 1-2 feet per minute. Reducing the coal char flow rate increases the amount of time that the coal char is exposed to water.

As shown in FIGURE 1, the present invention provides several improvements which optimize coal char rehydration. For example, the water spray apparatus 112 is strategically positioned within the rotary cooler 100 to maximize contacting of water spray with the coal char stream 126. The water spray nozzle 113 is positioned within the cooler 100 so that it faces the inlet end 128 of the cooler. This positioning of the water spray 112 within the rotary cooler 100 allows the coal char 126 to be sprayed as it is stirred by the rotation of the cooler.

The rotary cooler 100 stirs the coal char using two distinct stirring mechanisms which increase the amount of coal char surface area exposed for rehydration. First, as the rotary cooler 100 rotates, the coal char 126 is stirred by interacting with the heat exchanger tubes 102. The stirring mechanism provided by the tubes 102 is non-abrasive and therefore does not adversely diminish the particle sizes of the coal char 126. Second, as the rotary cooler 100 rotates, the coal char is raised by the lifters 122 and contacted

directly by the water sprayed from the water coming out of the nozzle 113 of the water spray apparatus 112 at position 132. These two stirring mechanisms greatly increase the amount of coal char surface area exposed for spraying which in turn maximizes the rehydration effects.

Wetting of coal char is therefore accomplished in the present invention using both direct and indirect contact of water spray with coal char. The interior surface of the rotary cooler 100 and the heat exchanger tubes 102 are moistened by water sprayed from the water spray apparatus 112. Indirect contact of water to coal char is provided by the heat exchanger tubes 102 and the interior surface of the rotary cooler 100. Direct contact of water to coal char is provided by the water spray apparatus 112.

As described above, it is well known that dry coal produces heat energy when exposed to water (either in a liquid or vapor form). When dry coal char is rehydrated, an exothermic reaction is produced which produces heat energy. The amount of heat energy produced is directly proportional to the porosity of the coal. Drying and pyrolysis of coal char leads to a much more developed pore structure in the coal, which leads to an increased amount of heat energy during rehydration. Experiments have shown that the heat energy produced during rehydration with water vapor may be sufficient to raise a 10% water, 90% coal mixture by as much as 300° F.

The rehydration process is therefore potentially self-limiting. As the coal char temperatures increase due to the rehydration process, the water adsorbed by the char evaporates, thus reducing the moisture content of the coal char. Therefore, if the heat created by the rehydration process is not compensated or removed from the coal char, the rate of rehydration and the probability of obtaining equilibrium moisture levels within the coal, making the coal safe for transport, is greatly diminished. The increased coal char temperatures caused by rehydration can result in non-uniform rehydration causing the formation of random hot spots on the coal char, which in turn can react with atmospheric oxygen to further the self-heating effect. Therefore, to maximize the

moisture levels of coal during rehydration, and to minimize the processing times, the coal char must be cooled during rehydration.

Thus, the present rotary cooler 100 solves the problems encountered by prior art rehydration systems by removing the heat energy produced during rehydration. The coal char 126 is simultaneously cooled by the heat exchanger tubes 102 as it is rehydrated by the water spray apparatus 112. The beneficial effects of rehydration are thereby maximized because the coal char can be rehydrated in less time than in prior art rehydration systems.

In the preferred embodiment of the rotary cooler 100, several rehydration process conditions are controlled by the plant control system which is described in more detail below with reference to FIGURE 3. For example, the retention time, the temperatures and atmospheric pressures within the rotary cooler, the cooling fluid flow rate, the cooling fluid temperature, the PDF flow rate, the rehydration rate, the moisture content of the coal, and the oxygen content of the atmosphere within the rotary cooler are all conditions controlled by the PCS (FIGURE 3). The position of the water spray apparatus 112 downstream from the inlet 106 is also dependent upon some of these factors.

In the preferred embodiment, the PDF flow rate ranges between 30,000 pounds per hour (pph) to 50,000 pph. To maximize the rehydration effect, the water spray apparatus 112 is preferably positioned at a point where the coal char temperature is reduced to 150" F. The distance that the water spray 112 is positioned downstream from the inlet 106 depends upon two factors: (1) the temperature of the coal char aggregate 126 as it enters the rotary cooler 100 at inlet 106, and (2) the flow rate of the coal char within the cooler. For example, given a PDF inlet temperature of approximately 300" F and a PDF flow of 30,000 pph, the water spray apparatus 112 is preferably positioned 10 feet from the inlet 106. Alternatively, given a PDF inlet temperature of approximately 400" F and a PDF flow of 50,000 pph, the water spray apparatus 112 is preferably positioned 17 feet from the inlet 106. For a PDF inlet temperature of approximately 500" F and a PDF

flow of 50,000 pph, the water spray apparatus 112 is preferably positioned 20 feet from the inlet 106.

In the preferred embodiment, the rehydration rate is approximately 8% (plus or minus 2%). The rotational speed of the cooler is approximately 0.75 to 1.5 revolutions per minute. In addition, the oxygen level content within the cooler is suppressed to reduce the risk of coal/char dust ignition and explosion. In the.preferred embodiment, the cooler 100 has a ventilation and fugitive dust control system which controls the gas flow through the cooler 100. The oxygen content in the cooler can range between 2% and 14%, but is preferably maintained at 8%.

The vessel of the rotary cooler is preferably equipped with suitable seals which allow control of the atmosphere within the rehydration vessel. The present rehydration process can be performed at atmospheric pressure. To reduce the coal char temperature at the outlet 108 to a desirable output range of between 70" F and 110" F, the cooling water in the exchanger tubes 102 should be maintained between 60" F and 95" F, and is preferably maintained at 60" F. Given a PDF flow rate of 40,000 pph, and a PDF feed temperature of 425" F, the flow rate of the cooling water should be maintained at 380 gallons per minute. The water flow to the water apparatus 112 is maintained at approximately 440 pph. Given these parameters, the PDF is rehydrated to approximately 7.5% moisture content by weight with a compensated energy release of 30 BTU per pound of PDF.

It is well known that the coal equilibrium moisture at about 75% relative humidity is considered safe to handle for storage and transport. In this condition, further moisture adsorption occurs only when the average ambient relative humidity exceeds 75%. Therefore, the present rotary cooler 100 preferably rehydrates the PDF by adding 6 to 10 grams of moisture to 100 grams of PDF. The coal char exiting the outlet 108 of the cooier 100 should therefore have a moisture content after rehydration in the range between about 7% to 9% by weight. At this point, the solid fuel is expected to be safe

for handling without excessive dilution of the high caloric value of the coal resulting from pyrolysis.

Referring now to FIGURE 2, an alternative embodiment of the rotary cooler of the present invention is shown having a multi-stage rehydration arrangement. As shown in FIGURE 2, the coal char 126 is rehydrated in multiple stages, using a plurality of lifters

122 and water sprayers 112. By wetting the coal char 126 in multiple stages, the rehydration process temperature can be controlled more precisely by the present rotary cooler 100. Stages or multiple points of rehydration result in the control of the rehydration process temperature at about 100" F.

As shown in FIGURE 2, the multi-stage embodiment of the present rotary cooler uses

3 spray nozzles 113 optimally spaced apart along the centeriine 114 of the rotary cooler 100. Each water nozzle is positioned within the cooler 100 so that water spray is directed against the flow of the coal char, i.e., toward the feed or inlet side of the rotary cooler 100. Similar to the single-stage cooler of FIGURE 1, the multi-stage cooler is inclined so that coal char is forced by gravity from the inlet end 128 of the cooler to the outlet

108. As the coal char 126 is transported toward the outlet 108 due to the force of gravity and the rotation of the cooler, the lifters 122 positioned on the inside of the cooler lift coal char particles into the air. As the particles are lifted by the lifers 122, they fall back to the char bed under the force of gravity and pass the spray positions 132. This allows full coverage of the coal char particles as they are sprayed by water by the water sprayers

112 at positions 132.

Similar to the single-stage rehydration cooler of FIGURE 1, the spray nozzles 113, the bracket 120, and the water supply line 116 all rotate with the rotary cooler 100 about the centeriine 114 during rehydration. Water is supplied to the water sprayers 112 through the water supply line 116 which enters the rotary cooler through a rotary union 118. The rehydration process control conditions discussed above are used in the multi-stage rehydration cooler shown in FIGURE 2.

As the number of water apparatus stages increases, there is a greater assurance that all of the char coal in the cooler will have the desired residence time. In order to uniformly rehydrate the coal char 126, it is desirable that the coal char 126 have a uniform residence time. As discussed above, under conditions requiring uniform residence time, the coal char should be fed into the rotary cooler in the correct ratio with respect to the rate that rehydration water is fed into the cooler. The plant control system regulates the rate that coal char is fed into the cooler and the rate of coal char flow to ensure that the correct ratio of coal char and water is fed into the cooler.

Referring now to FIGURE 3, a schematic diagram of a control system 200 for the coal rehydration cooler 100 of FIGURES 1 and 2 is shown. As described above with reference to FIGURE 1, the rotary cooler 100 can use both clean and reclaimed water to rehydrate coal char. Over time, reclaimed water becomes "dirty" or "oily." Therefore, unless coal debris is removed from the water, the water supply line 116 and water nozzle 113 can become plugged by the oily rehydration water supply. As shown in FIGURE 3, the preferred embodiment of the present invention uses a filter station 202 to remove solid coal particles from the water supply.

Both process water 204 and oily water 206 are filtered by the filter station 202. Both water supplies pass through the filter station 202 to remove solid particles which can potentially clog the spray nozzle 113. As shown in FIGURE 3, the filter station 202 comprises two dual-filter systems, an oily water dual-filter system 208 and a process water dual-filter system 210. Both filter systems 208, 210 are valved on both the inlet and outlet of the filter systems. Pressure transmitters 212 are positioned on the inlet and outlet side of the filter systems 208, 210. The pressure transmitters 212 allow a plant control system (PCS) 226 to determine when the rehydration water supply should be switched from one filter to the other to maintain a desired water pressure. For example, assuming that the rotary cooler uses the process water supply 204 for rehydration, the pressure transmitters 212 allow the PCS 226 to determine when to switch between the filter 214 and the filter 216.

As shown in FIGURE 3, shut-off valves 218, 220, positioned downstream from the dual- filter systems 208, 210, allow users of the rotary cooler 100 to switch between the process water 204 and oily water 206 supplies. In one preferred embodiment, the shut-off valves are implemented with solenoid valves which are controlled remotely by the PCS. If process water is desired, the oily water supply shut-off valve 220 is activated to stop the flow of oily water. Similarly, if oily water is desired, the process water shut-off valve 218 is used to shut off the process water. An alternative embodiment of the present invention uses no filters. When no filters are used, the plugging problem described above is avoided by using a water spray apparatus 112 specifically designed to avoid plugging the nozzle 113. An alternative water spray apparatus 112 is described in more detail below with reference to FIGURES 4a-4c.

The flow rate of rehydration water is controlled by the PCS 226 using a flow indicating controller (FIC) 222. The PCS 226 applies a rehydration water flow remote set point to the FIC 222 via a control line 224. The output of the FIC 222 controls a flow valve (FV) 228. A flow element (FE) 230 measures the flow rate of the rehydration water from the filter station 202 through the water supply line 116. The flow rate measured by the FE 230 is transmitted as a feedback signal to the FIC 222 by a flow transmitter (FT) 232. The FIC 222 balances the position of the flow valve 228 to maintain the rehydration water flow rate at the desired set point established by the PCS 226. Various inputs 234 to the PCS 226 determine the remote set point asserted on control line 224.

Mixing of continuous flowing streams requires that the various feed streams be fed into the mixer in the correct ratio. The PCS 226 controls the ratio that rehydration water, coal char, and cooling water is fed into the rotary cooler 100 to optimize the rehydration process. The rehydration ratio, the coal char feed rate, and the coal char yield are input to the PCS 226 at input 234. Based upon these inputs, the PCS 226 either calculates the correct ratio of rehydration water flow rate to coal char flow rate, or the ratio is pre¬ determined and stored in look-up tables in the PCS 226. Given a desired ratio, the PCS 226 calculates and controls the rehydration water flow rate required at any point in time

to achieve optimum rehydration conditions. The water flow rate is controlled by the PCS 226 by controlling the set point signal to the FIC 222. If the ratio varies, the PCS 226 compensates by appropriately adjusting the set point over control line 224.

The PCS 226 also monitors and controls the operation of the cooling system and the heat exchanger tubes 102. The PCS 226 monitors the temperature difference between the temperature of the coal char when it enters the cooler at the inlet 106 and when it exits the cooler at the outlet 108. The temperature of the coal char at the inlet 106 is measured by a temperature transmitter (TT) 236 and transmitted to the PCS 226 over a feedback line 238. Similarly, the temperature of the coal char at the outlet 108 is measured by a temperature transmitter (TT) 240 and transmitted to the PCS 226 over a feedback line 242.

As shown in FIGURE 3, the PCS 226 monitors the temperature of the cooling fluid using two temperature transmitters (TT) 244 and 246. The TT 244 measures the temperature of the cooling fluid as it enters the cooling system of the rotary cooler 100 and transmits the measured temperature to the PCS 226 over a feedback line 248.

Similarly, the TT 246 measures the temperature of the cooling fluid as it exits the cooling system of the rotary cooler 100 and transmits the measured temperature to the PCS 226 over a feedback line 250. Based on these two temperatures readings, and the char input and output temperature readings from TTs 236 and 240, the PCS 226 determines whether the heat exchanger tubes 102 are sufficiently cooling the coal char. The PCS 226 determines the optimum cooling fluid flow rate to optimize the rehydration process, and accordingly establishes a cooling fluid flow rate set point. The remote set point is transmitted to an FIC 252 over a control line 254.

Similar to the operation of the FIC 222, FT 232, FE 230 and FV 228, used to control the rehydration water flow rate, the PCS 226 controls the cooling fluid flow rate using the

FIC 252, an FT 256, FE 258 and FV 260. The FIC 252 accepts input from the PCS 226 and controls the flow valve 260 according to the set point transmitted from the PCS 226.

The flow element 258 measures the actual flow rate of the cooling fluid into the heat exchanger tubes 102. The flow transmitter (FT) 256 transmits the measured cooling fluid flow rate to the FTC 252, which adjusts the control signal to the FV 260 sp that the actual flow rate measured by the FE 258 equals the flow rate established by the PCS 226 via the set point.

The PCS 226 is a computerized control which implements a plurality of pre-defined algorithms. One set of algorithms monitor coal char input and process conditions in order to calculate the PDF feed flow rate through the cooler 100. The temperature of the coal char feed stream can optionally be measured directly using temperature sensors or can be predicted by the PCS 226. The temperature of the coal char feed stream can then be controlled by the PCS 226 by adjusting the flow rate of the coal char, the rehydration flow rate, and the cooling fluid flow rate. The combination of the coal char flow rate and the temperature of the rehydration system feed stream forms a knowledge base from which the PCS 226 operates. The knowledge base is used by the PCS 226 to allow it to appropriately control the setpoints over control paths 224 and 254 (the rehydration water flow remote setpoint and the energy compensation remote setpoint, respectively). By establishing remote the setpoints, the PCS 226 controls the rehydration water and the cooling fluid flow rates.

During typical operation, the rehydration ratio is determined from look-up tables based upon a process severity versus rehydration ratio basis. Alternatively, the moisture content of the rehydrated char discharge stream can be continually monitored using microwave moisture and radiation solids density sensors to provide a feedback signal to the PCS 226 which is indicative of the moisture content of the discharged PDF. Moisture and density sensors are well known in the art and are available from Berthold, Inc., a German company having an office in Pittsburg, Pa. In this alternative embodiment, the PCS 226 uses the feedback signal to control the operation of the cooler to produce a desired moisture content within the discharged PDF. Conventional algorithms using proportional,

integral, and derivative (PED) approaches can be used by the PCS 226 to control the PDF moisture content.

The coal char feed stream temperature is controlled in an upstream char quench process vessel (not shown). The PCS serves as a system integrator and has wide ranging control capabilities. In this case, the char temperature entering the rehydration rotary cooler is maintained in the quench. The char outlet temperature is controlled by modulation of the cooling fluid temperature and flow rate.

As described above with reference to FIGURE 1, the plurality of spray nozzles 113 tend to become clogged with coal debris when the rehydration system uses an oily water supply created when rehydration water is reclaimed after several rehydration processes. One solution, as described above with reference to FIGURE 3, uses filter systems to clean the reclaimed water. A disadvantage of filter systems is that the filters require frequent replacement as they become dirty. Replacement of these filters increase the operational costs associated with rehydration. In addition, if the filters go unchecked and are used for a period of time in a dirty or clogged condition, the effectiveness of the rehydration system is diminished. Eventually, the rehydration water supply may need to be flushed and the water supply replenished, further increasing rehydration operational costs. Therefore, a need exists for a water spray apparatus which can be used in a filter-less rehydration system using an oily water supply yet remain unplugged. The preferred alternative embodiment of the water spray apparatus 112 which solves the plugging problems described above is shown in FIGURES 4a-4d.

An oscillating water distributor 300 shown in FIGURE 4a is supplied water via water supply line 116. The water distributor 300 rotates with the rotary cooler 100 to evenly distribute water at a constant rate over the rotating dry coal char bed (shown above with reference to FIGURES 1 and 2):

The water distributor 300 is preferably comprised of abrasion-resistant carbon or stainless steel. In the illustrated embodiment, the water distributor 300 is affixed to the heat exchanger tubes 102 with fasteners (not shown). Alternatively, the water distributor 300 is affixed directly to the interior surface of the rotary cooler 100 with stainless or carbon steel fasteners. The water distributor 300 has two water distribution discs 302, 304, which are preferably spaced apart by a distance of approximately 1.5 inches using a plurality of small spacer dowels 306. During use, as the distributor 300 rotates within the cooler 100 water from the water supply line 116 enters the distributor 300 through an opening (not shown) in the center of the water distribution disc 302. Water is thereby forced into the space 308 between the discs 302, 304 and is discharged at the bottom of the space 308 when the discs 302, 304 are vertically aligned as shown in FIGURE 4a. Water discharged from space 308 continues to be supplied to the distributor as the cooler 100 and supply line 116 are rotated about the centeriine 114. As shown in FIGURE 4a, a water trough 310 is formed about the perimeter of the water distributor 300 by two weirs 312, 314, which are positioned substantially parallel to each other. The serrated weirs 312, 314 use

3/4 inch serrations to ensure that water is uniformly distributed to the coal char bed.

As water is supplied to the water distribution discs 302, 304, water is forced into the water trough 310 at the portion of the water distributor 300 which faces the coal char bed (not shown). More specifically, as the water distributor 300 and the water distribution discs 302, 304 rotate with the rotary cooler 100, water is driven by the force of gravity into the trough 310 formed into the bottom of the water distributor 300. The rotation of the water distributor 300 creates 2 wetting areas 320, 322 along the bottom of the rotary cooler 100 which rehydrate the coal char (not shown) as it is transported through the cooler 100. The wetting areas 320, 322 are preferably 18 inches wide.

As shown in FIGURES 4a-4d, the height and width of the water trough 310 varies along the circumference of the water distributor 300. However, the cross-sectional area of the trough 310 is held constant. The cross-sectional area of the trough 310 is held constant to ensure that a constant volume of water is held in the trough which in turn ensures that

the water exits the distributor 300 at a constant rate. Therefore, as the width of the trough 310 increases along the circumference of the water distributor 300, the height of the trough 310 and serrated weirs 312, 314 decreases, and vice versa. For example, the widest portion 324 of the trough 310 is shown at the bottom of the water distributor 300 in FIGURE 4a, and the narrowest portion 326 of the trough 310 is shown at the top.

As shown in FIGURE 4b, the trough 310 height is minimal at the widest portion 324 of the trough 310, and the height is maximal at the narrowest portion 326 of the trough 310. As the distributor 300 rotates about the rotary cooler centeriine 114, the width and height of the trough 310 at the bottom of the distributor 300 will vary inversely to one another. As the width of the trough 310 varies from its maximum to minimum value, the wetting areas 320, 322 will oscillate between two wetting points 328 (when the maximum width of the trough 310 is at the bottom of the distributor 300 as shown in FIGURES 4a and 4b) and 330 (when the minimum width of the trough 310 is at the bottom of the distributor 300, FIGURES 4a and 4b rotated 180°).

The design of the oscillating water distributor 300 provides a water spraying apparatus that self-cleans as it rotates. As shown in FIGURE 4d, a plurality of middle deflector paddles 332 are positioned inside and along the center of the distributor 300. The middle deflector paddles 332 preferably are angled along a center 335 of the middle paddles 332 in order to direct any unwanted coal char debris which may fall into the water trough 310 away from the narrow portion of the trough 310 toward the widest portion of the trough

310.

As shown in FIGURE 4d, a plurality of lifting paddles 333 are positioned inside the distributor 300 and along the perimeter of the distributor 300 substantially adjacent the weirs 312, 314. As the distributor is rotated about the centeriine 114, any coal char material that is forced into the widest portion of the trough 310 by the middle deflector paddles 332 is raised to the top of the distributor 300 by the lifting paddles 333 due to the rotation of the distributor 300. The char debris subsequently is allowed to drop to the cooler char bed as it clears the narrower portion of the trough 310 at the bottom of

the distributor 300. Using the water distributor 300 of FIGURES 4a-4d, the problems caused by plugged water nozzles are eliminated. Therefore, the rehydration coolers described above with reference to FIGURES 1-3 can use reclaimed oily rehydration water supplies without the need for expensive filter systems. Further, the present oscillating distributor uses the differential motion between the rotating distributor and the sliding coal char to ensure that the coal char is uniformly rehydrated.

A number of embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiment, but only by the scope of the appended claims.