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Drying Characteristics of a Greenhouse Type Solar Kiln

M. A. Sattar
Director (Ex.)
Seasoning & Timber Physics Division, Bangladesh Forest Research Institute, Chittagong.

Abstract/ Executive Summary:

The paper deals with the drying characteristics for a simple solar heated wood seasoning kiln. Four hardwood species were dried in four mixed charges in the kiln throughout the year. The attainable temperature and relative humidity were determined both inside and outside the solar kiln. The drying rate and drying time were evaluated for the solar, air and steam heated methods. The solar kiln was found effective in drying timber throughout the year.

Keywords: Drying characteristics, Hardwood, Relative humidity, Drying rate, Solar kiln, Chapalish

Location:

Start Date: 00-00-0000

End Date: 00-00-0000

Program Area: Postharvest and Agro-processing

Commodity: Wood

Objectives:

To evaluate the full technical viability of the BFRI solar kiln.

Methodology:

Four important indigenous wood species, viz., chapalish (Artocarpus chaplasha), champa (Michelia champaca), garjan (Dipterocarpus turbinatus) and mango (Mangifera indica) were selected for the study. The former three species are forest species used for furniture, joinery, construction and other purposes. The fourth species is a common homestead species used for furniture and construction purposes in the villages. Green timber in the log form was procured and converted into planks of 4 cm ´ 20 cm ´ 2 m dimensions. Six representative planks of each species were taken as sample boards for each charge of drying. Four charges were dried covering the four seasons-winters, post-winter, monsoon and post-monsoon. Air drying was undertaken simultaneously with solar drying in the open yard adjacent to the solar kiln. Another batch of identical timber was dried in a compartment type steam heated kiln of 3.0 m³capacity.

The initial moisture content of each of the sample board was determined by the oven dry method. The oven dry weights of all the samples were ascertained on the basis of the initial moisture contents. The daily progress of drying was recorded by weighing the samples at the end of day’s drying in the evening. Solar drying was started by operating the blower fan at 7.30 am every day and continued till the sunset. The inlet and outlet vents were opened 2 – 4 times a bay for 30 – 45 minutes till the timber was dried to 10 – 12% mc. Air drying was continued till the timber reached 12% mc during all the drying seasons except in the monsoon when the timber did not dry below 18-20% mc. Conventional steam kiln drying is not affected by the climatic conditions of any season, and as such one charge was dried following the standard kiln drying schedule.

Source of Information: Bangladesh Journal of Forest Science, Vol : 21 (1 & 2), Jan-July 1992, 20-31

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The solar kiln maintained a substantially higher temperature throughout the year compared to the ambient temperature. It could retain an average day temperature of 52 to 56⁰C which was sufficient for satisfactory drying of timber.A higher relative humidity and lower temperature are needed during the early stages of drying. The solar kiln maintained automatically a similar drying schedule. Proper operation of the vents obviated the necessity of extra humiditification.The higher temperature followed by a lower humidity caused a faster evaporation of moisture from the wood. A markedly higher rate of drying, and thereby lower drying time was found in the solar dried timber compared to those of the air dried timber. The season of the year affected significantly both solar and air drying. Solar kiln was effective throughout the year for drying of timber.

Knowledge Management: Journal