Wood drying chamber

Contents

Paper

Introduction

1 Equipment design and operation principle

1.1 Device and operation principle of drying chamber VK-

1.2 Construction and operation of auxiliary equipment

2 Selection and substantiation of drying and moisture-heat treatment modes

2.1 Selection of drying modes

2.2 Selection of initial heating and moisture-heat treatment modes

3 Process calculation

3.1 Calculation of drying cycle duration

3.2 Calculation of the number of drying chambers

3.3 Development of dryer plan

4 Thermal calculation

4.1 Determination of vaporised moisture mass

4.2 Determination of drying agent parameters

4.3 Determination of heat consumption for drying

4.3.1 Heat flow rate for initial heating

4.3.2 Heat losses through fences

4.3.3 Total heat flow

4.4 Determination of coolant flow rate

5 Process Development

5.1 Dryer Plan

5.2 Process Management

5.3 Process Control

Conclusion

List of used literature

Paper

The course project consists of an explanatory note and 1 sheet of graphic material (A1). The explanatory note includes pages 56, tables 13, figures 3, information sources 9.

TIMBER, DRYING, AGENT OF DRYING, HEAT CARRIER, DRYING CAMERA, MODE, CALENDAR, TECHNOLOGY, PLAN OF THE SHOP.

The purpose of the course project is to develop a sawmill based on BK4 drying chambers.

The apparatus of the drying chamber BK4 has been studied and described. Auxiliary equipment is described, their technical characteristics are given. The modes of drying, initial heating, and moisture treatment of lumber from wood are justified and selected: birch, spruce and pine. Process settlement has been performed. It is established that 5 cameras are required to run the program. Auxiliary equipment was selected. Based on the thermal calculation, the need for a drying shop in steam was determined. Plate and ribbed pipes are used for installation in chambers. A plan for the lumber drying workshop and process has been developed. The procedure of process control is given.

Introduction

Drying is the process of removing moisture from wood by evaporation.

The physical essence of the drying process is that the heated air is directed to the raw material when in contact with which it gives off its heat and itself cools. Moisture in wood, due to the perception of heat, turns into a vaporous state.

The purpose of drying: conversion of wood from natural raw materials into industrial material, with specific improved biological and physical and mechanical properties.

Process Tasks:

1. Making wood biologically resistant.

2. Increased strength of wood (dry wood can better withstand mechanical load).

3. Conversion of natural material into industrial material with simultaneous improvement of dried material quality in minimum time.

The main technological objectives of drying wood material are:

1. Reduction of formability and warpage of the material.

2. Reduction of wood weight by 1.5-2 times.

3. Protection of wood from damage by insects, rot and fungi and other tree-destroying organisms.

4. Increasing the service life of wood.

5. Improved performance of subsequent technological operations.

For drying lumber, there are the following methods of drying wood:

1. Convective gas-steam.

2. Convective atmospheric.

The gaseous drying agents may be:

- atmospheric air;

- flue gases;

- water vapor.

The importance of high-quality drying of wood is extremely high. It is predetermined by the need for enterprises to produce high-quality products in all respects, and most importantly by the resource of its operation.

The weakly controlled drying process also results in significant losses due to the occurrence of large warping of the dried material, cracking, internal deformations and, in this regard, reduced accuracy of its mechanical processing. It is absolutely not permissible to violate the drying technology of lumber - early unloading from the chamber in an out-of-drained state. This leads to its irrational use and exacerbation of wood deficiency.

Process Development

5.1 Dryer Plan

According to the project, the drying workshop covers an area of ​ ​ 1728 m2.

The workshop is equipped with five VK4 cameras located in a row. According to the design, the side wall, the end wall - with a control corridor and a traverse corridor located in the heated room.

For the convenience of controlling the cameras, it was decided to arrange a control corridor with a total area of ​ ​ 61 m2. A traverse path runs along the front of the chambers on the side of the doors.

The site for forming a stack with an area of ​ ​ 130.8 m2 has three pairs of rail tracks (for supplying lumber, forming or disassembling stacks, as well as a rail track for spare tracks). The middle of the rail tracks is interrupted by a pit in which a stacking elevator is installed. The raw lumber warehouse has two pairs of rail tracks (to accommodate four stacks) and covers an area of ​ ​ 114.7 m2 of dry lumber - four pairs of rail tracks (to accommodate eight stacks) with a total area of ​ ​ 232.2 m2. The dry lumber warehouse is separated by a wall from the stacking area.

5.2 Process Management

Transport and handling operations, mechanisms applied:

Transport means the combination of transport operations, vehicles and the system of organization of transport works in the drying shop.

The main transport operations include the supply of lumber to be dried at the stacking site; forming drying stacks; rolling stacks into and out of the chamber; feeding stacks to the dry lumber warehouse and placing them in the warehouse; disbanding of drying stacks; supply of finished products to the warehouse. The movement of stacks laid on track trolleys is carried out using a cable-block system and a mobile winch. The trolley itself is driven by an individual drive. Lumber stacks are laid on low two wheeled trolleys - tracks.

An essential condition for proper operation of the drying chamber is the proper stacking of lumber, which significantly reduces the percentage of scrap from warping and cracking, and contributes to a more even drying of the material, that is, a reduction in the drying time. The stack is composed of boards of one rock and one section. The thickness deviation shall not exceed + 5 mm.

Pine pads made of straight-layer wood without knots of the same thickness are used for reliable clamping of all boards in the stack. The length of the gaskets used is strictly equal to the width of the formed stack (not more than 1.8 m), their width is 35-40 mm, thickness is 25 mm. Stacks are formed with gaskets of equal width. Only dry gaskets are used, calibrated by construction on one side on a raisemus machine with a humidity of the corresponding final moisture of the dried wood, but not more than 12%. The distance between the gaskets along the length of the stack depends on the wood, the thickness and width of the material, the final humidity, the required drying quality and the length of the dry parts to be drilled. Gaskets are located perpendicular to the length of boards. The lower gasket shall be above the support bar or over another strong base. Extreme gaskets at face flat end of stack are laid flush with end faces of boards. Laying without sleepers is more rational, since the capacity of the stack increases, its aerodynamic drag decreases.

All formed stacks must be full-weight in height, they are laid out on a mark so that the gap between the top of the stacks and the bottom of the chamber overlap is not more than the thickness of the board with the gasket.

The stacks formed must correspond to the overall dimensions in width and height, respectively, 1.8 and 2.6 meters (minor nearest deviations are allowed downwards depending on the cross section of the dried lumber), as well as be no more than 6.5 m in length. It is allowed to dry different gradients together only with the same estimated duration of their drying.

Before drying, the chambers are prepared: they are cleaned of various garbage, it is necessary to clean the heaters from dust, lubricate the bearings, check the serviceability of doors and heaters. Serviceable heaters are heated in 1015 minutes. Valves must reliably close the system. To check the operation of the humidifying pipes, it is necessary to let steam through the pipe and, if clogged holes are revealed, clean them. Operation of condensate traps, condition of fan plant are checked, at that it is established whether there is run-out of shaft and knock in bearings. Psychrometer and remote control system are examined and prepared.

After checking the condition of the equipment, the chamber must be warmed up and only then can the lumber stacks be loaded. If the lumber is loaded into cold chambers, moisture will condense on the enclosures and equipment during heating, causing metal corrosion.

The stack formed on the track car must be fed along the rails to one of the drying unit chambers or in the absence of a free chamber to the raw lumber warehouse. To roll stacks from one rail track to another, as well as to load and unload drying chambers, a traverse trolley is used.

The stack from the loading platform is rolled up onto a traverse trolley along the rail track laid on its platform. The level of rails of this track exactly corresponds to the level of the head of rails of transport and cornel tracks. The stacked trolley moves along the front of the chambers and stops against the chamber to be loaded. After stopping the trolley against the desired chamber, it is manually adjusted to align the rails of the traverse trolley with the rails of the chamber and locked, after which the stack is rolled into the chamber. Unloading stacks from the chamber is carried out in reverse order.

After loading the stacks into the chamber, the first process operation of the drying process is carried out - initial heating of the wood. Then, according to the specified mode, the drying process itself is carried out, during which the condition of the drying agent is continuously monitored and the moisture of the wood and internal stresses in it are periodically monitored.

Air humidity in the chambers is controlled by supply channels and humidifying pipes. If you want to increase the humidity of the air in the chamber, you need to close the vanes on the supply and supply channels. When the humidity of the air and with closed vanes does not reach the preset mode, simultaneously with closing the vanes, it is necessary to additionally let steam into the chamber through humidifying pipes. If it is necessary to reduce the humidity of the air in the chamber, the supply channels are opened and the humidifying pipes are closed.

When adjusting the mode, do not forget about the thermal inertia of the chamber.

The transition from one degree to another should be carried out smoothly, since a sharp change in temperature and humidity can cause dangerous stresses in the material, which in turn can cause cracks.

Before drying, final moisture-heat treatment is performed to relieve residual internal stresses. The drying quality is then checked. This is followed by unloading stacks from the chamber and preparing it for the next cycle.

Conclusion

A project of a sawmill was developed to dry spruce, pine and birch lumber in the amount of 26500 thousand m3 per year to humidity equal to 12%. The proposed construction site Minsk region.. The workshop is located indoors, with a total area of 1728 m2

5 drying chambers of VK4 grade are proposed for installation. The capacity of each of them is 57.6 m3 of conventional material. Chambers are arranged in one row, along traverse paths. Stacks are formed and disassembled manually using elevator L6,515. To transport stacks, I choose rail transport, to deliver lumber to the stacks, an ET26.5 trolley is used.

The chambers are equipped with cast-iron ribbed pipes. Heat carrier-steam with pressure of 0.35 MPa. The workshop's annual coolant demand is 11663.9 t/year.