RU2554455C1 - Drying method of sawn timber in convective drying chambers and device for method's implementation - Google Patents

Abstract

FIELD: woodworking industry.

SUBSTANCE: drying method of sawn timber in convective drying chambers provides for the maintenance of specified parameters of a circulating drying agent. For that purpose, the floor temperature of the drying chambers is equalised to the temperature of side and ceiling structures of the drying chambers by using some part of hot water wasted in heating units of the drying chambers. And a floor heating device is made in the form of a coil of a metal-reinforced plastic pipe and installed under the floor of the drying chambers at the distance of 15-20 cm from the floor surface. The coil of the metal-reinforced plastic pipe is made of at least two loops and a bypass loop along the perimeter of the drying chamber floor with a possibility of maintaining the sufficient temperature of heating water from heating devices, thus considering the length of each loop.

EFFECT: invention shall provide for the improvement of sawn timber drying conditions.

3 cl, 1 dwg, 1 tbl

Description

The invention relates to methods for drying sawn softwood and hardwood and can be used in woodworking enterprises.

There is a method of drying lumber in a batch chamber dryer by heat and moisture treatment of lumber with monitoring the state of the drying agent according to the temperature of wet and dry thermometers (Aut. St. USSR 1717916, class F26B 3/04, 03/13/1989). According to this method, acute saturated steam is additionally supplied to the chamber until the temperature in the chamber reaches 75-90 ° C and at this temperature heat and moisture treatment of the material is carried out for 2-6 hours, after which the steam is stopped. Then, atmospheric air is additionally fed into the chamber, lowering the temperature with a wet thermometer until a psychrometric difference of 4-5 ° C is obtained, the material is kept in this mode for 2-3 hours, after the entire heat and moisture treatment cycle is repeated, the psychrometric difference is increased to 6- 8 ° C. After the third cycle, exposure is carried out for 8-24 hours until a psychrometric difference of 18-28 ° C is achieved. Then, the final heat and moisture treatment is carried out, and the temperature during the drying process is kept constant.

However, the known method of drying lumber is very complex.

A well-known shaft dryer containing shafts with upper and lower rows of inlet and outlet ducts located in them, respectively connected to an air distribution chamber and outlet chambers between the shafts, heating and suction fans (Aut. St. USSR 1703933, class F26B 17/12, 12/25/1989). The dryer is equipped with an exhaust system, and the lateral and lower sides of each supply duct are perforated. Above the inclined faces of each of the boxes an additional triangular divider is installed with the formation of a cavity. Each cavity is connected to its heating fan by means of an air duct, while the inclined faces are brought out of the side faces of the ducts. The total area of perforation of the side faces of the supply ducts in the upper rows is greater than in the lower ones.

A disadvantage of the known dryer is the difficulty of maintaining the specified parameters.

According to patent RU 2027127, cl. F26B 3/04, 05/14/1992, there is a known method of drying lumber by pre-heating it with subsequent drying. Preliminary heating of the material is carried out without the influx of fresh air when the energy carrier is supplied to the air heater and the circulation of heated air in the drying volume. Drying is carried out cyclically. alternating the mode of supply of fresh air to the drying volume and energy in the air heater. during the circulation of heated air in the drying volume with the mode of complete cessation of the supply of fresh air to the drying volume, the energy source in the heater and the circulation of heated air in the drying volume. After that, the material is additionally maintained in the ventilation mode without supplying fresh air to the drying volume and energy carrier to the air heater.

However, the known method involves drying in steps, the transition to which requires careful control of the current moisture content of the lumber.

By author St. USSR 1021891, class F26B 3/04, 02/09/1982 there is a known method of drying lumber of various thicknesses by continuously mixing batches of lumber stacked in stacks to meet the flow of a heated drying agent and maintaining the set temperature of the latter. The temperature of the drying agent according to the "dry" thermometer is maintained the same for batches of lumber of any thickness. The psychrometric difference is maintained the lower, the thicker the lumber with its reduction by 1-3 ° C during the transition to drying a batch of lumber of increased thickness.

The disadvantage of this method is that it does not take into account the nature of the developing internal stresses in lumber, leading to the formation of cracks, warping, as well as an increase in drying time.

The objective of the invention is to improve the quality of dried lumber, simplify the drying method, increase productivity and efficiency of the drying process.

The technical result when using the invention is to improve the drying regime of lumber, to create a device for implementing the drying method.

The specified technical result is achieved by the fact that the method of drying lumber in convective drying chambers provides for maintaining the specified parameters of the circulating drying agent. For this, the floor temperature of the drying chambers is equalized to the temperature of the side and ceiling structures of the drying chambers by using some of the hot water used in the heaters of the drying chambers. A device for floor heating is made in the form of a coil from a metal-plastic pipe and is installed under the floor of the drying chambers at a distance of 15-20 cm from the floor surface. The coil of the metal-plastic pipe is made of at least two circuits and a bypass circuit along the perimeter of the floor of the drying chamber with the possibility of maintaining a sufficient temperature of heating water from the heaters, taking into account the length of each circuit.

Figure 1 is a simplified diagram of a device for implementing the method of drying lumber.

The device is made in the form of a coil made of a metal-plastic pipe. The coil includes a bypass circuit 1 along the perimeter of the floor of the drying chamber and two circuits 2 and 3. The pipes of all circuits are connected to the heaters (not shown in the diagram).

The invention is illustrated by the following examples.

Example 1. The proposed method of drying pine lumber with a thickness of 50 mm and a length of 6 m in convection drying chambers using the device for this method consists of heating the chamber and lumber, heating the lumber, drying itself, leveling the final moisture content of the lumber, and cooling the lumber in the chamber.

A device for implementing the drying method is constantly connected to heating water and turns off only when the ambient temperature rises to + 15 ° C. Moreover, the first bypass circuit 1 is laid around the perimeter of the drying chamber of FIG. 1 to equalize the floor temperature in the first zone (at a distance of 1 m from the camera enclosure) and the temperature of the chamber enclosures. The second and third circuits are also permanently connected and maintain the floor temperature on the side and in the center of the chamber. Direct and return hot water are connected to the same system as the heaters of the drying chamber. As a result, a complete floor covering of the drying chamber is created with an additional supporting thermal device.

The heating process of the drying chamber is reduced by an average of 10% in the warm period and by 14 ... 27% due to the heat accumulated by the monolithic reinforced concrete slab of the floor of the drying chamber, lying on a metal-plastic pipe into which hot water is supplied.

Lumber heating is carried out with closed supply and exhaust channels. If the drying chamber has a cold floor, condensation will form on it from the moisture of the circulating air. The drying agent is drained, and the drying process begins on the unheated material, internal stresses occur in the wood and, as a result, defects such as microcracks on the edges and edges of the sawn timber. Such materials, for example, are not suitable for further gluing.

The drying process of lumber consists of several stages, each of which is characterized by certain operating parameters. The stiffness of the regime at a given temperature determines the relative humidity of the drying agent of lumber.

The use of the device ("warm floor") for the specified drying method allows you to maintain the parameters of the drying modes within the specified limits, which helps to reduce the drying time to 12 ... 20% on almost all thicknesses of lumber. Comparative indicators of drying lumber with the use of the device and without it (traditional execution of the floor of the drying chamber) are given in the table.

Cross sections of pine lumber, mm The decrease in the duration of drying of lumber,% Transition of lumber to lower grades due to drying defects,% without cold floor device with the device "warm floor" without cold floor device with the device "warm floor" cold season summer period cold season summer period 50 × 150 one one 12.69 18.7 11,2 4.3 Note*. The data array for the period from August 2013 to October 2013 was processed at the enterprise Angel-Elite LLC, Krasnoyarsk

Example 2. The proposed method of drying larch lumber 50 mm thick and 6 m long in convection drying chambers using the device for this method consists of heating the chamber and lumber, heating the lumber, drying itself, leveling the final moisture content of the lumber, and cooling the lumber in the chamber.

A device for implementing the drying method is constantly connected to heating water and turns off only when the ambient temperature rises to + 15 ° C. Moreover, the first bypass circuit is laid around the perimeter of the drying chamber, item 1, to equalize the floor temperature in the first zone (at a distance of 1 m from the camera enclosure) and the temperature of the chamber enclosures. The second and third circuits pos. 2 and 3 are also connected constantly and maintain the floor temperature in the chamber itself.

For the quality of drying of larch lumber, the period of heating of the drying chamber and heating of the lumber is responsible. According to GOST 19773-84, when drying larch lumber, there are especially stringent requirements for the relative humidity of the drying agent in the initial period of heating the lumber. During this period, drying of lumber due to the occurrence of surface microcracks is unacceptable.

The lumber is loaded into the drying chamber when the heating water is turned on in all 3 loops of the coil of the device for implementing the method of drying lumber.

Lumber is heated with closed supply and exhaust channels to create the maximum possible relative degree of saturation of the drying agent.

The process of drying lumber consists of several stages, each of which is characterized by certain operating parameters. The stiffness of the regime at a given temperature determines the relative humidity of the drying agent of lumber.

A device for implementing the drying method (the "warm floor" system) in the drying chamber allows you to maintain the parameters of the drying modes within the specified limits, which helps to reduce the drying time to 20% on almost all thicknesses of larch lumber.

The process of conditioning or leveling the final moisture in the presence of a warm floor is more smooth with preserving the specified quality of drying lumber.

The transition to the lower grades is reduced to 4 ... 10% due to the reduction of such drying defects of larch as warping, violation of integrity (cracks), uneven final moisture content of dried lumber.

Reducing the drying time of lumber reduces the cost of drying while increasing the productivity of drying chambers.

Claims (3)

1. A method of drying lumber in convective drying chambers, comprising maintaining the specified parameters of the circulating drying agent, characterized in that the floor temperature of the drying chambers is equalized to the temperature of the side and ceiling structures by using some of the hot water spent in the heaters of the drying chambers. 2. A device for implementing the method according to claim 1, comprising a system of piping circuits connected to air heaters, characterized in that it is made in the form of a coil from a metal-plastic pipe and is installed under the floor of the drying chambers at a distance of 15-20 cm from the floor surface. 3. The device according to claim 2, characterized in that the coil of the metal-plastic pipe is made of at least two circuits and a bypass circuit along the perimeter of the floor of the drying chamber with the possibility of maintaining a sufficient temperature of the heating water from the heaters, taking into account the length of each circuit.