Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Patent
1996-01-25
1997-08-26
Sollecito, John M.
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
34489, 34496, 34500, 34504, 34619, 34623, 34636, F26B 700
Patent
active
056599757
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION
This is a national phase of PCT/EP94/102479 filed Jul. 27, 1994 which is based upon German national application P43 26 877.3 of Aug. 11, 1993 under the International Convention.
In the drying of boards, particularly building boards, such as gypsum plaster boards or mineral-fiber boards, the boards transported through a drier are brought into contact with heated air.
The supply of drying air can be done through longitudinal ventilation, cross ventilation or cross ventilation with nozzles. In the case of longitudinal ventilation the drying air is supplied at one end of the drier, or, when the latter is subdivided into several zone at one end of a zone, and evacuated at the opposite end.
In the case of cross ventilation the air is supplied at several locations on the sides of the drier and evacuated at the opposite sides, whereby it is possible to achieve larger mass flows of drying air through the drier. The largest air mass flows can be guided in the case of cross ventilation via nozzles through the so-called nozzle drier.
In most cases, an air recirculation process is used, wherein a large part of the drying air is recirculated. This drying air, also called recirculated air, is heated outside the inner drier space. Only a small part of the drying air is discharged as outgoing air and a part corresponding to the outgoing air is supplied from outside as fresh air.
For warming the drying air, e.g. through burners, optionally through damper registers, fuel i.e. primary energy is needed, and for the supply of air by fans electric energy, i.e. secondary energy is needed. The primary energy as well as the secondary energy, estimated to be three times as costly, should be kept as low as possible.
In the DE-Z Zement-Kalk-Gips, No. 8 1991, Pages 421 to 425 a process for the drying gypsum wall-building boards with cross ventilation is described, wherein a lower consumption of primary energy is achieved by using the condensation heat of the outgoing air. For this purpose in each of the two drier zones the hot air is cooled down in a heat exchanger arranged between the drier pipes for preheating of the hot air. Since the hot air, i.e. the drying air supplied to the board, is heated only to low temperatures, a large mass flow of drying air is needed. This leads to a relatively high consumption of secondary energy.
A further drying process wherein a low consumption of primary energy is achieved by using the condensation heat of the outgoing air is known from DE-A 26 13 512. This process is a two-stage process. In the first drying stage high temperatures and high air humidity are used and in the second drying stage low temperatures and low humidity are used. The drying efficiency of the first stage is two or three times greater than that of the second stage and the second drying stage is heated by the outgoing air of the first drying stage, due to the interposition of a heat exchanger. In both stages the drying air is supplied in a recirculation process, namely in the first drying stage in the form of a longitudinal ventilation and in the second stage in the form of cross ventilation with a large mass flow of recirculated air. The large recirculated air mass flow of the second stage and the resulting high consumption of secondary energy are the reasons why in practice this process has been replaced by the process of the invention.
In the generic drying process known from the book "Trocknungstechnik" by K. Kroll and W. Kast, Third Volume, 1989, Pages 489 to 493, gypsum plaster boards which are guided through the drier on decks, are also dried in two stages at high temperature but at average humidity of the drying air in the first stage and with average temperature and low humidity of the drying air in the second stage. In the generic drier two zones are provided for performing the first stage and one zone is provided for performing the second stage. This and the higher temperatures of the drying air in the first stage lead to the assumption of a higher drying efficiency in the first
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Bahner Friedrich
Braun Manfred
Lang Karl-Friedrich
Lehn Gerhard
Maurer Karl
Babcock BSH AG
Dubno Herbert
Gravini Steve
Sollecito John M.
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