JPH04190085A - Hot air drying method - Google Patents

Abstract

PURPOSE:To reduce heat loss in a hot air drying facility by a method wherein highly humid gas, discharged after drying process, is dehumidified by a gas separating film and is circulated again into the drying processing unit of a material to be processed as gas for drying. CONSTITUTION:Air for drying, which flows out of a heat exchanger 12, is blown against strip copper plates 16, penetrating through a processing material receiving unit 15 in a drying chamber 14. Wet gas, blown against the strip copper plates 16, flows out of the drying chamber 14 and is supplied to a water vapor separator 13 through a blower 11 after becoming gas proximated to the saturating condition of about 90-100 deg.C. The water vapor separator 13 is provided with a gas separating film 17 and removes the water vapor corresponding to the total amount evaporated from the strip copper plates 16 and the like selectively. Dry gas, not permeated through the gas separating film 17, enters a heat exchanger 12 and the temperature of the same is risen to about 120 deg.C without causing deterioration of temperature substantially.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hot air drying method used in the steel manufacturing, food, valve, printing industries, etc.

[Prior art and its problems] Cleaning treatment is required in the cold rolling process, pickling one culm, etc. in a steel manufacturing line. In order to prevent rust from forming, the steel plates after the cleaning treatment are immediately forced to dry before being transferred to the next process.

As a drying method here, hot air drying using heated air is generally used. FIG. 2 is an explanatory diagram showing the configuration of a typical conventional hot air drying facility. In the figure, 1 is a floor. Drying air is supplied from the floor 1 to the heat exchanger 2. The air supplied to the heat exchanger 2 is heated to about 120° C. and then supplied to the drying chamber 3.

The air blown onto the strip steel plate 4, which is the object to be treated, in the drying chamber 3 is discharged to the outside as it is.

Note that such hot air drying equipment is used as a dryer not only in steel manufacturing lines but also in manufacturing lines for food products, valves, printing industries, and the like.

In the hot air drying method performed by such hot air drying equipment, the used gas air containing a large amount of water vapor is not reused but is discharged outside in a high temperature state. This results in a heat loss of about 30 kcal/N13, resulting in a huge energy loss in places such as steel mills that require large amounts of hot air treatment.

In order to solve such problems, attempts have been made to recover heat from the above-mentioned exhaust gas. However, with this method, the temperature of the exhaust gas is as low as about 100 to 200° C., making efficient heat recovery difficult, and it has not been put into practical use.

The present invention has been made in view of this point, and can efficiently remove water vapor in exhaust gas, reuse the removed dry gas, and drastically reduce heat loss in hot air drying equipment. A hot air drying method is provided.

[Means for Solving the Problems] The present invention provides a drying process by supplying a drying gas heated to a predetermined temperature to an object to be processed, and then passing the high-humidity gas discharged after the drying process through a gas separation membrane. This hot air drying method is characterized in that the drying gas is dehumidified by the drying gas, and the drying gas is circulated again as the drying gas to the drying processing section for the object to be processed.

[Operations] According to the hot air drying method according to the present invention, water vapor is selectively separated from high temperature and high humidity exhaust gas by using a gas separation membrane. Then, after dehumidifying and drying the exhaust gas without significantly lowering its temperature, the exhaust gas is recycled and used as a drying gas. This dramatically reduces heat loss in hot air drying equipment.

[Examples] Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram showing the configuration of hot air drying equipment used in a steel manufacturing line to which the method of the present invention is applied. In the figure, 11 is a blower that supplies drying air to the heat exchanger 12. A steam separator 13 is interposed between the blower 11 and the heat exchanger 12. The heat exchanger 12 is configured to heat the drying air to about 120° C. and then supply it to the object storage section 15 in the drying chamber 14 . That is, the drying air that has exited the heat exchanger 12 is blown within the drying chamber 14 onto the strip steel plate 16 that is inserted through the object housing section 15 . The wet gas blown onto the strip steel plate 16 becomes a nearly saturated gas at approximately 90 to 100°C, then leaves the drying chamber 14 and is supplied to the steam separator 13 again via the blower 11. ing. The water vapor separator 13 has a gas separation membrane 17 and is configured to selectively remove the entire amount of water vapor evaporated from the strip steel plate 16 and the like. Then, the dry gas that does not pass through the gas separation membrane 17 remains almost unchanged in temperature.
It enters the heat exchanger 12 and is heated again to about 120°C. Here, when removing water vapor using such a gas separation membrane 17, in order to increase the partial pressure difference between the water vapor contained in the supply side gas and the permeation side gas, which exist through the gas separation membrane, the permeation side A large amount of dry gas (
For this purpose, it is necessary to flow some of the non-permeable gas (using dry air or the like) or to reduce the pressure on the permeate side. However, adopting such a method is extremely uneconomical as it results in loss of product gas and the need for extra energy. Therefore, in the present invention, attention is paid to the fact that the non-dehumidified gas is hot and humid and that the dry gas is not required to be highly dehumidified, and the atmosphere is used as it is as the purge gas on the permeation side.

As a result, a sufficient dehumidification effect can be obtained with a low-energy blast of about 11 blowers. The performance of the gas separation membrane 17 is as follows: water vapor and air (N2) separation coefficient α>500;
Water vapor permeation rate RH2o>1xl O-'Cm3 (
STP)/cm' -see-cmHg or more is preferable, more preferably α>1000, RH20>lXl0-
3cm' (STP)7cm2·sec-cmHg. Incidentally, even if a gas separation membrane with a performance lower than this is used, the process will still work, but the membrane area will become large and two-stage separation will become necessary, which will be economically disadvantageous.

In this way, in this hot air drying method, the wet gas leaving the drying chamber 14 is passed through the blower 11 and returned to the steam separator 13.
After selectively removing water vapor from the gas separation membrane 17, the gas is supplied to the heat exchanger 12 again. In other words, the exhaust gas used is recycled and used as a drying gas after dehumidifying and drying without significantly lowering the temperature of the exhaust gas. As a result, heat loss in hot air drying equipment can be drastically reduced.

[Effects of the Invention] As explained above, according to the hot air drying method according to the present invention, water vapor in the exhaust gas is efficiently removed, the removed dry gas is reused, and the heat of the hot air drying equipment is This has remarkable effects such as being able to drastically reduce losses.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the configuration of hot air drying equipment used in a steel manufacturing line to which the method of the present invention is applied, and FIG. 2 is an explanatory diagram showing the configuration of a conventional hot air drying equipment. 11... Blower, 12... Heat exchanger, 13...
Steam separator, 14... Drying chamber, 15... Processed object housing section, 16... Odd lip steel plate, 17... Gas separation membrane.

Claims (1)

[Claims] After drying the object by supplying a drying gas heated to a predetermined temperature, the high-humidity gas discharged after the drying process is dehumidified by a gas separation membrane to turn it into dry gas, and the dry gas is recycled again. A hot air drying method characterized in that the drying gas is circulated to a drying processing section for the object to be processed.