Drying and gas or vapor contact with solids – Apparatus – With means to treat gas or vapor
Patent
1986-03-14
1987-10-20
Makay, Albert J.
Drying and gas or vapor contact with solids
Apparatus
With means to treat gas or vapor
34119, 34124, F26B 1318
Patent
active
047004932
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a control apparatus for controlling the differential pressure between steam inlet and outlet lines of a web dryer. More particularly, this invention relates to a control apparatus for controlling such differential pressure between a steam inlet and outlet line of the drying section of a paper machine.
INFORMATION DISCLOSURE STATEMENT
In a papermaking machine, a formed web passes throughh a paper drying section immediately after passing through the pressing section. Such drying sections include a plurality of rotating heated cylinders over which the wet paper web passes in order that the web may gain the required degree of dryness. More particularly, in conventional drying sections, the wet web is passed around the outside of steam-heated, cast iron drying cylinders. The steam used to heat these drying cylinders enters the dryer through hollow journals by means of rotating seals and it condenses on the inside of the dryer shell or cylinder. As the steam condenses on the internal surface of the rotating cylinders of the dryer, such condesnate is evacuated by means of a siphoning assembly. However, when such drying cylinders are operated at high speeds, such as 1,000 to 1,200 feet per minute web speed, which is not unusual in drying sections, the condensate does not collect at the bottom of the dryer but rather is thrown by centrifugal forces around the inside surface of the dryer cylinder or shell. Such disposition of the condensate within the dryer shell is known in the art as the "rimming phenomenon" and is fully described in an article published by TAPPI 1958, volume 41, No. 2 by R. E. White. When the condensate is rimming, the dryer shell is not exposed to "live steam" but is insulated from the live steam by the condensate layer which impedes the transfer of heat from the live steam to the surface of the dryer shell and subsequently to the adjacent paper web. Such insulation reduces the drying process and this resistance to heat transfer can be kept to a minimum by decreasing the depth of the layer of condensate within the dryer shell.
The accumulation of non-condensible vapors inside the dryer shell can give rise to non-uniformities in the drying characteristics of the dryer shell along the cross machine direction. This problem has been set forth by R. B. Hurm, as published in TAPPI, volume 46, No. 9, 1963. Such buildup or accumulation of non-condensible vapors or gases can be kept to a minimum by continuously allowing some of the uncondensed vapor or steam to be evacuated from the dryer shell together with the condensate. This uncondensed vapor, or blow-through is then able to entrain the non-condensible gases and keep such gases from accumulating in the dryer shell.
Additionally, such blow-through steam can have the secondary and beneficial effect of reducing the pressure differential between the inlet and outlet lines of the dryer shell, such pressure differential being required to evacuate the condensate. The low density blow-through steam entrains and mixes with the high density condensate to form a two-phase mixture with a resultant density substantially less than the condensate. The pressure differential required to evacuate this relatively low density mixture of steam and condensate against the centrifugal force caused by rotation of the dryer shell is then correspondingly reduced. Furthermore, this blow-through steam can be used in further dryer shells of the drying section that require lower pressure steam. Alternatively, such blow-through steam can be boosted or supplemented to increase the pressure thereof to be reused in the same dryer shell provided, of course, the pressure differential across the dryer shell is not too large.
A further consideration in condensate evacuation is the requirement of stability of operation. In practice, it has been observed that condensation evacuation may cease if the outer tip of the siphon pipe adjacent the condensate becomes submerged by condensate. In this event, the dryer may fill with condensate so th
REFERENCES:
patent: 2696679 (1954-12-01), Cram
patent: 2869248 (1959-01-01), Justus
patent: 2885790 (1959-05-01), Cram
patent: 2992493 (1961-07-01), Fishwick
patent: 4222178 (1980-09-01), Moran
patent: 4447964 (1984-05-01), Gardner
patent: 4493158 (1985-01-01), van Os
patent: 4499668 (1985-02-01), Jumpeter
Fosler Robert C.
Garvin, Jr. Stanley P.
Wedel Gregory L.
Archer David J.
Beloit Corp.
Campbell Raymond W.
Makay Albert J.
Veneman Dirk J.
LandOfFree
Dryer differential pressure controller does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dryer differential pressure controller, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dryer differential pressure controller will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1605040