Drying plant and method for drying wood

Details Drying plant and method for drying wood Drying plant and method for drying wood

2002-04-15

2004-04-27

Lazarus, Ira S. (Department: 3749)

Drying and gas or vapor contact with solids

Process

With nondrying treating of material

C034S518000, C034S077000, C034S092000

Reexamination Certificate

active

06725566

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
Applicants claim priority under 35 U.S.C. §119 of Russian Application No. 99122270, filed Oct. 27, 1999. Applicants also claim priority under 35 U.S.C. §365 of PCT/RU00/00419 filed Oct. 24, 2000. The international application under PCT article 21 (2) was not published in English.
TECHNICAL FIELD
The invention relates to drying equipment and can be used in timber industry, woodworking and other branches of industry, whenever parameters and procedures necessary to dry materials as wood are used.
Prior Art
Drying plants are known from prior art that include a batch-operating drying chamber and a furnace located near it, in which woodworking waste products may be and are primarily used as fuel to generate heat necessary for drying. Usually, the furnace gases or a mixture of furnace gases with air are used in such systems (e.g., see, Spravochnik po sushke drevesiny (Wood-drying reference book) edited by E. S. Bogdanov, Moscow, Lesnaya promyshlennost, 1990, pp. 38-63, patent RU 2105941, and the following inventor's certificates: SU:380454, JP09223628, JP11094460, JP11201639, JP11241883). While using those systems, accompanying problems inevitably appear due to the following facts. Gaseous combustion products of high-temperature wood burning consist largely of CO
2
, H
2
O and nitrogen oxides NO
x
. The situation becomes much more complicated when an incomplete fuel combustion takes place, because in this case the combustion products are fouled not only with soot (i.e., unburned carbon particles), but also with dry distillation products as well, consisting of CO and a number of hydrocarbons, which are usually chemically active, smell specifically, have relatively low temperatures of boiling, etc. Furthermore, there is a risk of environmental pollution due to a possible formation of dioxins and furans as a result of condensation reactions, when gaseous products of wood burning are cooled with the presence of even minimal amounts of chlorine (although furnace ashes do not contain these products).
As a result, to ensure ecological safety of the drying plants and to produce high-quality dry wood materials, considerable expenses are required to purify combustion products and drying agents. Besides, special devices are required to provide necessary drying conditions (e.g., different humidifiers or steam generators are used to maintain the necessary level of humidity), resulting in a sophisticated design, higher prices and complicated maintenance. Nevertheless, neither the measures taken nor considerable expenses can guarantee either necessary ecological safety or high quality of dried materials.
Specification
The subject of the present invention is to ensure higher ecological safety and provide a highly productive, power-saving drying process, allowing to produce high quality dried materials. The proposed drying plant is not expensive, simple in maintenance and does not require highly qualified personnel. The drying plant can be installed either in existing premises or in the form of a separate premise, e.g. at lumbering sites.
The proposed drying method is as follows: stack the wood into the free internal space of the drying chamber, close the chamber, and supply a hot drying agent (the air heated in the pipes located in the furnace flue) into the chamber. The woodworking waste products are the primary fuel used in the furnace. The air is forcedly circulated from pipes located in the furnace flue to the lower part of the free internal space of the drying chamber, and from the upper part of the free internal space of the drying chamber into the pipes of the furnace flue, and backwards. During drying, a portion of cooled and humidified air from the upper part of the free internal space of the drying chamber is forcedly supplied into the condensate cleaning unit, where it is mixed with the furnace gases, which are also forcedly supplied into the unit for purification; on their way to the cleaning unit, the furnace gases pass through a cavity located in the bottom of the drying chamber providing additional heating of the chamber. Air circulation from the pipes of the furnace flue to the lower part of the free internal space of the drying chamber and from its upper part into the pipes located in the furnace flue, and forced supply of furnace gases through an exhaust pipe into the cavity in the bottom of the drying chamber and then into the condensate cleaning unit, as well as forced supply of a portion of cooled and humidified air from the upper part of the free internal space of the drying chamber into the condensate cleaning unit, is realized with the aid of three appropriate exhaust ventilators. The pressure in the free internal space of the drying chamber falls slightly during drying. Humidity conditions can be adjusted by releasing vapor from the upper part of the free internal space of the drying chamber into atmosphere.
Temperature conditions can be regulated by adjusting air circulation intensity from the pipes of the furnace flue to the lower part of the free internal space of the drying chamber and from the upper part of the free internal space of the drying chamber into the pipes; temperature conditions can also be regulated by adjusting the temperature of the drying agent (air), which depends on burning intensity and the amount of fuel in the furnace.
The proposed method for drying wood may be realized as a drying plant consisting of a heat-insulated drying chamber with a free internal space, a furnace located close to the drying chamber, and facilities for supplying drying agent from the furnace into the drying chamber. The bottom of drying chamber is designed with two cavities horizontally arranged and hermetically separated from each other. The partition between these cavities is made of diathermic material. The lower cavity in the bottom of the drying chamber is designed in such a way as to provide forced feeding of furnace gases into the cavity from the exhaust pipe of the furnace flue. The upper cavity located in the bottom of the drying chamber is designed in such a way as to provide supply of the air heated in the furnace flue into the cavity; in the upper cavity, the heated air is distributed among air distribution channels to interact with the material to be dried located in the free internal space of the drying chamber at specially arranged places. There is a possibility to provide forced feeding of a portion of the air cooled and humidified during drying from the upper part of the free internal space of the drying chamber into the furnace flue. Besides, the drying plant is equipped with a condensate cleaning unit located outside the drying chamber; the furnace gases are forcedly fed into the unit after they pass through the lower cavity in the bottom of the drying chamber; also, a portion of cooled and humidified air is forcedly fed into the unit from the upper part of the free internal space of the drying chamber for mixing up with the furnace gases to form a condensate; after that, the purified air is exhausted into atmosphere.
The facilities that forcedly supply furnace gases from the exhaust pipe of the furnace flue to the lower cavity in the bottom of the drying chamber and into the condensate cleaning unit after they pass through the lower cavity, are designed in the form of the first exhaust ventilator (smoke exhauster) located outside the drying chamber and condensate cleaning unit and connected to the outlet of the lower cavity in the bottom of the drying chamber and to the inlet of the condensate cleaning unit.
The facilities that supply a portion of cooled and humidified air from the upper part of the free internal space of the drying chamber into the condensate cleaning unit are designed in the form of the second exhaust ventilator located outside the drying chamber and the condensate cleaning unit and connected to both of them.
The facilities that bleed a portion of cooled and humidified air from the upper part of the free internal space of the drying chamber and supply it into the furnace flue are designed in t

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