GB1567129A

GB1567129A - Heating of coal with microwave energy

Info

Publication number: GB1567129A
Application number: GB1502478A
Authority: GB
Original assignee: Foster Wheeler Energy Corp
Current assignee: Foster Wheeler Energy Corp
Priority date: 1977-05-02
Filing date: 1978-04-17
Publication date: 1980-05-08
Also published as: ES468913A1; JPS53136731A; AU3504878A

Description

(54) HEATING OF COAL WITH MICROWAVE ENERGY (71) We, FOSTER WHEELER ENERGY CORPORATION, a corporation organised and existing under the laws of the State of of Delaware, United States of America, of 110 South Orange Avenue, Livingston, New Jersey, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for heating coke, coal and coal char utilizing microwave energy, and more particularly, to the use of microwave energy to desorb sulfur dioxide from saturated char, coke or coal and to ignite coal, coke or coal char.

Hydrocarbon fuels, which are normally burned in industrial installations, such as coal and oil-fired power stations, contain sulfur which is normally converted to sulfur dioxide in the combustion process. Although in older installations the sulfur dioxide was vented to the atmosphere with the other effluent gases, recent air pollution control requirements have placed great emphasis on removing the sulfur dioxide from the gases before they are expelled into the atmosphere. One successful technique comprises contacting the sulfur dioxide containing effluent gas stream with a coal char which adsorbs the sulfur compound and converts it to sulfuric add. This adsorption step is followed by regeneration of the adsorbent to produce a gas stream having a high concentration of sulfur dioxide. Such a process is described in P.Steiner et al "Removal and Reduction of Sulfur Dioxides from Polluted Gas Streams", Advances in Chemisuy, No. 139 (1975).

Regeneration is achieved by heating the char to a temperature sufficient to convert sulfuric acid to sulfur dioxide, water and carbon dioxide, which gases are then removed from the reaction system. In the commercial process the saturated char is contacted with hot sand. The sand, which is merely an inert heat transfer medium, heats the char to the appropriate temperature to cause desorbtion of the SO2, approximately 12000F.

This regeneration process has a number of substantial disadvantages. First it requires special apparatus to heat the sand and to separate the regenerated char and the sand.

Second, the process is relatively inefficient since the char is heated indirectly. Moreover, reactors must be large and elevators are required to lift the sand and char.

It is an object of this invention to provide a method for heating or igniting coal, coke or char with microwave energy.

It is a further object of the present invention to provide a method of regenerating char, coke or coal used to adsorb sulfur dioxide from a gaseous stream which does not suffer from the disadvantages of the prior art techniques.

A more specific object of the invention is to provide a method, utilizing microwave energy, for regenerating char or coke used to adsorb sulfur dioxide from a gaseous stream.

These and other objects are achieved by subjecting char, coke or coal to microwave energy at a frequency which will cause arcing thereby oxidizing a portion of the carbon, thus, increasing the temperature of the coal, coke or char.

The above brief description, as well as further objects, features, and advantages, of the present invention will be more fully appreciated by reference to the following detailed description of a presently preferred, but nevertheless illustrative embodiment, when taken in connection with the accompanying drawing which is a schematic representation of a proposed apparatus for continuously regenerating coal using microwave energy.

Microwave heating in the 800--3,000 MHz frequency range has been widely used for cooking or reheating of food in microwave ovens. Frequencies of about 915 and about 2,450 MHz are the ones primarily used for this purpose, although frequencies of about 5,850 MHz and about 18,000 MHz are also available for microwave heating.

It has now been found that if a coal, char or coke is passed through a microwave field, it is rapidly heated to temperatures which are sufficient to desorb any adsorbed sulfur dioxide.

The char, coke or coal is heated to a temperature sufficient to regenerate a saturated char, coke or coal in a matter of seconds. This rate and magnitude of heating is substantially greater than that attained in microwave heating of food. The rapid rate at which the required high temperatures are reached is caused by violent arcing which occurs when the carbonaceous material is subjected to microwave energy. Small surface portions of the carbonaceous material are oxidized as a result of the arcing. It appears that this arcing is caused by the build up and discharge of electrostatic charges on char.

The regeneration can occur either in a batch process or, preferably, in a continuous system. In the batch process saturated material is placed in a microwave oven. The oven is turned on and the SO, fumes are exhausted for further processing. After the regeneration has been completed, the material is removed from the oven and replaced by additional saturated adsorbent. The time required to achieve the requisite desorption would depend upon many parameters, including the amount of adsorbent, the density and intensity of the microwave field and the spacing of the electrodes. It is anticipated that the heating cycle would require at least about 3 seconds, but less than about 5 minutes and preferably from about 30 to about 60 seconds.

EXAMPLE Coal char in the form of pellets 9 mm in diameter and 18 mm in length loaded with about 15% H2SO4 was placed in a Litton commercial microwave oven which operated at 2450 MHz. The pellets were placed in a glass container and positioned so that they were in contact with each other.

Shortly after the oven was turned on, visible arcing occurred. The pellets were heated to a red glow in a matter of seconds and SO2 gas was released.

After desorbtion was completed, analysis of the pellets indicated that all SO had been driven off.

The process can also be carried out con tinuously utilizing equipment similar to that used in commercial microwave heating in the food industry. Such equipment is well known in the art and is described in Bengtsson "Microwave Heating in the Food Industry", 62 Proceedings of the IEEE 44 (January 1974). The apparatus would, of course, have to be modified because of the peculiarities of coal processing and because of the evolution of sulfur dioxide. Such modification is clearly within the skill of the art as seen by Knapp United States patent No. 3,449,213 which describes apparatus useful for the pyrolysis of coal with microwave energy. (See in particular, Figure 3).

A suitable apparatus is shown schematically in the drawing. Saturated adsorbent is passed from hopper 1 onto a conveyor belt 2, which continuously moves the adsorbent through a microwave oven 3 (the microwave elements are not shown). In the oven the adsorbent is subjected to microwave energy which causes arcing and a rapid increase in temperature to about 12000F. At this temperature SO, and other gases are desorbed and removed from the oven via conduit 4 which conduit is connected to an exhaust fan or other appropriate means, not shown.

The exact parameters required to carry out the process continuously can be easily determined by those skilled in the art.

While the foregoing description is specifically directed to a process for regenerating spent char, it should be apparent to one skilled in the art that microwave energy can be used to heat char, coke or coal or to regenerate thermally other adsorbents for any purpose.

Moreover, it can also be used to heat coal and, specifically, to ignite coal, coke or char, whether or not such material has been used as an adsorbent. Thus, it can be used to start up a fluidized bed coal burning vapor generator by passing fluidized coal particles through a microwave field. Such a vapor generator is described in United States patent No. 3,823,693.

WHAT WE CLAIM IS: 1. A process for heating char, coke or coal comprising subjecting said char, coke or coal to microwave energy for a sufficient period of time to cause arcing whereby said char coke or coal is heated.

2. A process according to claim 1 wherein said microwave energy is applied at a frequency of 915, 2,450, 5,850 or 18,000 MHz.

3. A process according to claim 2 wherein said microwave energy is applied at a frequency of 915 or 2,450 MHz.

4. A process according to claim 2 wherein said char, coke or coal is subjected to said microwave energy for a period of from about 3 seconds to about 5 minutes.

5. A process according to claim 4 wherein said char, coke or coal is subjected to said microwave energy for a period of from about 30 seconds to about 60 seconds.

6. A process for igniting char, coke or coal comprising subjected said char, coke or coal to microwave energy for a period of time suffident to cause arcing whereby said char, coke or coal is ignited.

7. A process according to claim 6 wherein said microwave energy is applied at a frequency of 915, 2,450; 5,850 or 18,000 MHz.

8. A process according to claim 7 wherein said microwave energy is applied at a frequency of 915 or 2,450 MHz.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

It has now been found that if a coal, char or coke is passed through a microwave field, it is rapidly heated to temperatures which are sufficient to desorb any adsorbed sulfur dioxide.

The char, coke or coal is heated to a temperature sufficient to regenerate a saturated char, coke or coal in a matter of seconds. This rate and magnitude of heating is substantially greater than that attained in microwave heating of food. The rapid rate at which the required high temperatures are reached is caused by violent arcing which occurs when the carbonaceous material is subjected to microwave energy. Small surface portions of the carbonaceous material are oxidized as a result of the arcing. It appears that this arcing is caused by the build up and discharge of electrostatic charges on char.

The regeneration can occur either in a batch process or, preferably, in a continuous system. In the batch process saturated material is placed in a microwave oven. The oven is turned on and the SO, fumes are exhausted for further processing. After the regeneration has been completed, the material is removed from the oven and replaced by additional saturated adsorbent. The time required to achieve the requisite desorption would depend upon many parameters, including the amount of adsorbent, the density and intensity of the microwave field and the spacing of the electrodes. It is anticipated that the heating cycle would require at least about 3 seconds, but less than about 5 minutes and preferably from about 30 to about 60 seconds.

EXAMPLE Coal char in the form of pellets 9 mm in diameter and 18 mm in length loaded with about 15% H2SO4 was placed in a Litton commercial microwave oven which operated at 2450 MHz. The pellets were placed in a glass container and positioned so that they were in contact with each other.

Shortly after the oven was turned on, visible arcing occurred. The pellets were heated to a red glow in a matter of seconds and SO2 gas was released.

After desorbtion was completed, analysis of the pellets indicated that all SO had been driven off.

The process can also be carried out con tinuously utilizing equipment similar to that used in commercial microwave heating in the food industry. Such equipment is well known in the art and is described in Bengtsson "Microwave Heating in the Food Industry",

62 Proceedings of the IEEE 44 (January 1974). The apparatus would, of course, have to be modified because of the peculiarities of coal processing and because of the evolution of sulfur dioxide. Such modification is clearly within the skill of the art as seen by Knapp United States patent No. 3,449,213 which describes apparatus useful for the pyrolysis of coal with microwave energy. (See in particular, Figure 3).

A suitable apparatus is shown schematically in the drawing. Saturated adsorbent is passed from hopper 1 onto a conveyor belt 2, which continuously moves the adsorbent through a microwave oven 3 (the microwave elements are not shown). In the oven the adsorbent is subjected to microwave energy which causes arcing and a rapid increase in temperature to about 12000F. At this temperature SO, and other gases are desorbed and removed from the oven via conduit 4 which conduit is connected to an exhaust fan or other appropriate means, not shown.

The exact parameters required to carry out the process continuously can be easily determined by those skilled in the art.

While the foregoing description is specifically directed to a process for regenerating spent char, it should be apparent to one skilled in the art that microwave energy can be used to heat char, coke or coal or to regenerate thermally other adsorbents for any purpose.

Moreover, it can also be used to heat coal and, specifically, to ignite coal, coke or char, whether or not such material has been used as an adsorbent. Thus, it can be used to start up a fluidized bed coal burning vapor generator by passing fluidized coal particles through a microwave field. Such a vapor generator is described in United States patent No. 3,823,693.

WHAT WE CLAIM IS: 1. A process for heating char, coke or coal comprising subjecting said char, coke or coal to microwave energy for a sufficient period of time to cause arcing whereby said char coke or coal is heated.
2. A process according to claim 1 wherein said microwave energy is applied at a frequency of 915, 2,450, 5,850 or 18,000 MHz.
3. A process according to claim 2 wherein said microwave energy is applied at a frequency of 915 or 2,450 MHz.
4. A process according to claim 2 wherein said char, coke or coal is subjected to said microwave energy for a period of from about 3 seconds to about 5 minutes.
5. A process according to claim 4 wherein said char, coke or coal is subjected to said microwave energy for a period of from about 30 seconds to about 60 seconds.
6. A process for igniting char, coke or coal comprising subjected said char, coke or coal to microwave energy for a period of time suffident to cause arcing whereby said char, coke or coal is ignited.
7. A process according to claim 6 wherein said microwave energy is applied at a frequency of 915, 2,450; 5,850 or 18,000 MHz.
8. A process according to claim 7 wherein said microwave energy is applied at a frequency of 915 or 2,450 MHz.
9. A process according to claim 7 wherein

said char, coke, or coal is subjected to said microwave energy for a period of from about 3 seconds to about 5 minutes.
10. A process according to claim 9 wherein said char, coke or coal is subjected to said microwave energy for a period of from about 30 seconds to about 60 seconds.
11. A process for regenerating char, coke or coal having sulfur dioxide adsorbed therein in the form of sulluric acid comprising subjecting said char, coke or coal to microwave energy at a frequency that causes arcing for a sufficient period of time to increase the temperature of said char, coke or coal to a level at which said sulfuric acid is converted to sulfur dioxide and is desorbed from the char, coke or coal.
12. A process according to claim 11 wherein said microwave energy is applied at a frequency of 915 2,450, 5,850 or 18,000 MHz.
13. A process according to claim 12 wherein said microwave energy is applied at a frequency of 915 or 2,450 MHz.
14. A process according to claim 12 wherein said char, coke or coal is subjected to said microwave energy for a period of from about 3 seconds to about 5 minutes.
15. A process according to claim 14 wherein said char, coke or coal is subjected to said microwave energy for a period of from about 30 seconds to about 60 seconds.
16. A process according to claim 11 wherein said temperature is about 12000F.