System and method for using board plant flue gases in the production of syngas

Abstract

Disclosed is an apparatus and method for capturing the hot humid gases from a gypsum board dryer and utilizing those gases in the production of a synthetic gas (referred to as syngas). The syngas produced can then be utilized within a gypsum board plant to reduce the amount of natural gas needed. The method utilizes the heated water vapor (H.sub.2O) and carbon dioxide (CO.sub.2) found within the flue gas of a board dryer. The H.sub.2O and CO.sub.2 are used in a gasification process to yield the syngas.

Claims

1. A system for increasing construction board manufacturing efficiencies, the system comprising: a board dryer that includes at least one burner for heating a wet board and a stack to vent hot humid gases generated therefrom, the hot humid gases comprising water vapor and carbon dioxide (CO.sub.2); a return line coupled to the stack for capturing the hot humid gases from the board dryer; a gasifier for converting carbonaceous materials into a synthetic gas, the gasifier being coupled to the return line in such a way that the gasifier receives the hot humid gases from the return line, wherein the water vapor from the hot humid gases reacts with the carbonaceous materials to produce synthetic gas; and further wherein the carbon dioxide from the hot humid gases reacts with the carbonaceous materials to produce carbon monoxide (CO), the carbon monoxide (CO) increasing the energy content of the synthetic gas, the synthetic gas including carbon hydrogen, carbon monoxide (CO), and carbon dioxide; a supply line connecting the gasifier to the at least one burner in such a way that the hydrogen, carbon monoxide, and carbon dioxide from the gasifier can travel through the supply line to the at least one burner so that the hydrogen, carbon monoxide, and carbon dioxide fuel the burner for heating the wet boards.

2. The system as described in claim 1 wherein the dryer includes a series of four sequentially located dryer zones and wherein the stack and return line are positioned in such a way that they receive the hot humid gases from the second dryer.

3. The system as described in claim 1 further comprising supply lines for delivering the synthetic gas with increased energy content from the gasifier to the burner, whereby the synthetic gas with increased energy content is used in drying the wet board.

4. The system as described in claim 1 wherein the dryer includes a series of driers and supply lines connect the gasifier to each dryer of the series of driers to deliver the synthetic gas to each of the driers.

5. The system as described in claim 1 wherein the dyer includes a series of dryer zones and wherein the stack and return line are positioned in such a way that they receive the hot humid gases from the dryer zone having the highest humidity and wet bulb temperatures relative to the other dryer zones in the series of dryer zones.

6. A method for producing syngas comprising the following steps: drying wet construction materials via a burner, the drying creating water vapor and carbon dioxide; capturing the water vapor and carbon dioxide and mixing it with carbonaceous materials; gasifying the carbonaceous materials in the presence of the water vapor and carbon dioxide to produce a syngas including hydrogen gas, carbon monoxide, and carbon dioxide; and supplying the burner with the hydrogen gas, carbon monoxide, and carbon dioxide.

7. The method as described in claim 6 wherein the wet construction materials are gypsum building boards.

8. A system for making a gypsum building board, the system comprising: a gypsum board dryer including a burner that can heat a wet gypsum board to produce water vapor and carbon dioxide; a stack positioned about the board dryer in such a way that the stack receives the water vapor and carbon dioxide from the board dryer; a gasifier positioned in such a way that the gasifier receives the water vapor and carbon dioxide from the stack, the gasifier being configured to react a carbonaceous material with the water vapor and carbon dioxide to form a synthetic gas containing hydrogen, carbon monoxide, and carbon dioxide; and a supply line connecting the gasifier to the burner in such a way that the hydrogen, carbon monoxide, and carbon dioxide from the gasifier can travel through the supply line to the burner so that the hydrogen and carbon monoxide fuel the burner for heating wet gypsum boards.

9. A method for making a gypsum building board, the method comprising: heating a wet gypsum board with a burner of a gypsum board dryer to produce water vapor and carbon dioxide; forming a synthetic gas containing hydrogen, carbon monoxide, and carbon dioxide by providing the water vapor and carbon dioxide to a gasifier that reacts a carbonaceous material with the water vapor and carbon dioxide to form the synthetic gas; and supplying the synthetic gas to the burner so that the hydrogen, carbon monoxide, and carbon dioxide fuel the burner to heat wet gypsum boards.

10. The method of claim 9, further comprising combusting natural gas with the burner.

11. The system of claim 1, wherein the burner is a natural gas burner.

12. The method of claim 6, further comprising combusting natural gas with the burner.

13. The system of claim 8, wherein the burner is a natural gas burner.

14. The method of claim 6, wherein: the water vapor and carbon dioxide in the drying step are hot as a result of the drying step; and the water vapor and carbon dioxide are mixed with the carbonaceous materials while still hot from the drying step.

15. The system of claim 8, wherein the gasifier is positioned in such a way that the gasifier receives the water vapor and carbon dioxide from the stack while the water vapor and carbon dioxide are still hot from the gypsum board dryer.

16. The method of claim 9, wherein the the water vapor and carbon dioxide in the heating step are hot as a result of heating the wet gypsum board; and the water vapor and carbon dioxide are provided to the gasifier while still hot from the heating step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in connection with the accompanying drawings in which:

(2) FIG. 1 is a schematic diagram illustrating a multi stack board plant in accordance with the present invention.

(3) FIG. 2 is a schematic diagram illustrating a single stack board plant in accordance with the present invention.

(4) FIG. 3 is a flow chart illustrating the steps of the present invention.

(5) Similar reference characters refer to similar parts throughout the several views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(6) The present invention relates to utilizing the byproduct of a board plant in the production of a synthesis gas (referred to as syngas). The syngas produced by way of the present invention can then be utilized within the board plant to reduce the amount of natural gas needed. The method utilizes the heated water vapor (H.sub.2O) and carbon dioxide (CO.sub.2) found within the flue gas of a board dryer. The H.sub.2O and CO.sub.2 are used in a gasification process to yield syngas.

(7) Gasification is a process whereby carbon, from feed materials such as coal, wood, biomasses, or waste fuels is converted into high temperature water vapor, carbon monoxide (CO), and hydrogen (H). This process involves reacting feed materials with oxygen at high temperatures. Suitable waste fuels include anthracite culm, coal plant tailings, or gob piles. The gas produced from the gasification process is syngas, which can serve as a substitute for more conventional gases, such as natural gas. Syngas typically has an energy content of between 100-500 BTU per cubic foot. Gasification can be carried out at either elevated or atmospheric pressures.

(8) Water vapor is a critical element necessary for converting carbon into hydrogen gas (H.sub.2), as can be seen in the primary gasification reaction:
C+H.sub.2O.fwdarw.CO+H.sub.2(Equation 1)
The reaction of Equation 1 typically occurs at a temperature of between 1500-1800 F.

(9) The present invention utilizes water vapor from the stack of a conventional board plant to supply the H.sub.2O needed for the gasification reaction of Equation 1. Utilizing these board plant vapors is advantageous because the evaporated water is already in gaseous form and is, therefore, ready to react with the hot carbon. Also, an energy savings is realized in the gasification reaction because the vapor leaving the board plant is already heated, thereby eliminating the need to independently heat the vapor. The standard methods for water evaporation and air saturation or steam injection are not required.

(10) Another important component in gasification is carbon dioxide (CO.sub.2). Namely, the energy content of the resulting syngas can be increased by reacting carbon dioxide with carbon in accordance with the following equation:
CO.sub.2+C.fwdarw.2CO(Equation 2)
As with Equation 1, this reaction occurs at elevated temperatures (in order to maintain the temperature at 1500 of some of the carbon must be completely burned). The additional carbon monoxide (CO) produced via Equation 2 can be added to the syngas to slightly improve the BTU content. The additional carbon dioxide (CO.sub.2) needed for Equation 2 is likewise found within the flue gas of a board plant. Namely, the carbon dioxide (CO.sub.2) is recycled along with the water vapor (H.sub.2O). A typical board plant produces an off gas with a CO.sub.2 content of 3-6% on a dry basis. Carbon dioxide (CO.sub.2) is also produced during the combustion of syngas.

(11) A typical syngas produced in accordance with the present invention would have the constituents listed below in Table 1. However, this listing is representative of only one type of syngas that can be produced in accordance with the present method. The BTU content of this resulting gas would be between 100-210 BTU per cubic foot for an air blown system (and between 500-1000 BTU per cubic foot for an oxygen blown system).

(12) TABLE-US-00001 TABLE 1 CO.sub.2 3-5% H.sub.2 8-15% CO 30-35% C.sub.1-C.sub.5 Less than 1% O.sub.2 Less than 1% N.sub.2 Balance

(13) Thus, the present invention finds an advantageous use for one of the largest by-products in a gypsum board plantthe heated water vapor found in flue gases. For every two tons of gypsum board produced by a plant, one ton of water must be evaporated in the board dryers. The water content of the dryer is typically 0.3 to 0.4 lbs. of water (H.sub.2O) for everyone 1 lb of air. This means that small board plants release approximately 25 tons of water per hour while large ones can release over 60 tons per hour. Moreover, the dryer typically produces water at elevated temperatures due to the combustion of natural gas. Traditionally, the water vapor by-product is vented to the atmosphere and is not recovered. The present invention, instead of releasing this water vapor into the atmosphere recovers this gas and effectively uses it in the production of syngas.

(14) The system of the present invention saves tremendous amounts of energy. Namely, by recycling hot stack gas, as opposed to utilizing ambient air, a 100,000,000 BTU/hour gasifier would realize an energy savings of more than 13,000,000 BTU/hour. Even more energy savings are realized as the recycled carbon dioxide (CO.sub.2) is used to improve the BTU content of the syngas as noted above. The process loop of the present invention saves water and energy in addition to making for a more efficient gasification.

(15) An embodiment of the present invention 20 is illustrated in FIG. 1. As shown, a board dryer, such as a gypsum board dryer, is depicted with several dryer zones spaced in sequence. Each zone includes one or more burners 24 that are used to create the hot air necessary to dry the boards. In traditional dryers, burners 24 burn natural gas. The water is evaporated in the dryer zones (Nos. 1-4) and is delivered up one or more stacks 26. Fans (not illustrated) are included within each stack to remove the moisture from within the dryer. In accordance with the invention, instead of delivering the high humidity vapor into the atmosphere, it is captured by way of a return line 28 and a blower 32.

(16) Preferably, the gas is recovered from the second stack, as the second stack of a four zone dryer typically has the highest humidity and wet bulb temperatures. By utilizing the stack with the highest wet bulb temperatures, increased gasification efficiencies are realized. For example, the dry bulb temperature within the second stack may be in the range of 300 F. to 400 F., while the corresponding wet bulb temperature would be in the range of 170 F. to 200 F. This hot vapor, which includes a certain amount of carbon dioxide (CO.sub.2), is thereby delivered to gasifier 34 via blower 32. As is known in the gasification arts, the gasifier 34 includes a lower outlet 36 for ash or other combustion by-products. An outlet line 38 is also included for the syngas produced by the gasification. In the preferred embodiment, this outlet line 38 delivers the syngas to one or more of the burners 24. In this manner, the syngas produced by the present invention can be used to replace the need for natural gas, which is typically used for the burners. The syngas can be treated via wet electrostatic precipitators or wet scrubbers to remove tars or wood oils. A compressor can also be included within line 38 (either before or after being treated) for compressing the syngas. Such compression allows the gas to be more easily transported to a desired destination.

(17) FIG. 2 is another embodiment of the present invention. This embodiment is the same as the primary embodiment, but a single stack is included in the final dryer zone. The dry bulb temperature within the single stack may be in the range of 200 F. to 230 F., while the corresponding wet bulb temperature would be in the range of 150 F. to 185 F.

(18) FIG. 3 is a flow chart illustrating the various steps carried out in the method 40 of the present invention. These steps include an initial step 42 wherein a building material, such as a gypsum building board, is dried via a burner. This drying step creates a humid gas as the moisture from the building materials is evaporated. In the following step 44, the humid gases are captured and routed to a gasifier. During the gasification step 46, carbonaceous materials are burned along with the humid gases to yield synthesized gas or syngas. Finally, the syngas can thereafter be supplied, at step 48, to the burner for additional drying. In this manner, the overall energy efficiency of the method 40 is increased.

(19) The present disclosure includes that contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention.