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EP-4735813-A1 - WOOD KILN

EP4735813A1EP 4735813 A1EP4735813 A1EP 4735813A1EP-4735813-A1

Abstract

The present invention provides a kiln (1) that is unvented, relies on passive air circulation via natural convection, requiring no fan or similar means to provide a forced circulating airflow and uses passive gravity driven dehumidification. The wood is placed in a sealed kiln chamber (10) with no ventilation, which is well insulated. This improves the efficiency of the heating system and results in a drying method that uses the minimum amount of energy during the drying process to achieve the maximum dryness of the wood. The kiln (1) uses passive, gravity driven dehumidification, so the dehumidification device has no moving parts and is not powered in any way.

Inventors

  • Lansdowne, David

Assignees

  • Lansdowne Biotechnics Limited

Dates

Publication Date
20260506
Application Date
20240627

Claims (15)

  1. A kiln for drying wood using renewable energy having a kiln chamber (10) into which wood is placed and the renewable energy is used to heat air within the kiln chamber, characterised in that the kiln (1) is unvented, encapsulates an insulated kiln chamber (10) and a liquid medium (55) is heated by the renewable energy before being passed to a thermal store (40) at the bottom of the kiln (1), the thermal store (40) heats the floor (15) of the kiln chamber (10) thus heating the air therein and the heated air (16) rises and circulates around the wood (25) by natural convection, collecting water from the wood (25) as it rises to the top of the kiln chamber (10) as hot, water-filled air (17), where it leaves the kiln chamber (10), hits a nucleation point (75) that removes the water from the hot, water filled air (17) and the water leaves the kiln (1) separate from the air via a wicking means (80).
  2. A kiln for drying wood according to claim 1, wherein the nucleation point (75) forms part of a dehumidification device that removes water from the water filled air (17) )and the water is directed outside the kiln (1) whilst the air is retained within the kiln (1) and falls in a channel (20, 82) under gravity where it cools before re-entering the bottom of the kiln chamber (10) as cool air (18).
  3. A kiln for drying wood according to claim 1 or claim 2, wherein the renewable energy is solar energy collected by a solar panel (50) through which the fluid medium (55) is pumped by an electric circulation pump (60) that is powered by its own solar PV panel (65) selected to balance the power of the pump (60) automatically with the power obtained from the solar panel (50).
  4. A kiln for drying wood according to claim 3, wherein the solar panel (50) is contained within the same ground footprint as the kiln (1).
  5. A kiln for drying wood according to claim 3 or claim 4, wherein the solar panel (50) comprises an outer sheet (50) and inner sheet (52') encapsulating a gas or vacuum cavity (53) covering a heat absorbing unit (56) containing the fluid medium (55) and a heat absorption material (57) that enhances the heat retained by the fluid medium (55) from the solar energy.
  6. A kiln for drying wood according to claim 5, wherein the heat absorbing unit (56) has a lower plenum (58) to which cold fluid medium (55) is pumped by the pump (60) and a top plenum (59) from which the hot fluid medium (55) is returned to the thermal store (40) and both the lower plenum (58) and the top plenum (59) has a plurality of holes (54) to ensure laminar flow of the fluid medium (55) into a chamber housing the heat absorption material (57) through which the fluid medium (55) flows absorbing solar energy as it rises from the lower plenum (58) to the top plenum (59).
  7. A kiln for drying wood according to any of the preceding claims, wherein the fluid medium (55) is water.
  8. A kiln for drying wood according to any of the preceding claims, wherein the outer wall of the dehumidification channel (20) forming the cooler wall of the kiln (1) is composed of a plurality of horizontally arranged, overlapping panels (37) spaced from the panel (37) below by wicking material (80) to absorb condensate water exiting the kiln (1).
  9. A kiln for drying wood according to claim 8, wherein as the condensate water falls over the outside of the panel (37) below, it evaporates cooling the lower panel (37) and thereby multiplying the cooling effect of each panel (37).
  10. A kiln for drying wood according to any of the preceding claims, wherein the kiln (1) includes a simple indicator linked to the temperature of the wood, calibrated to show when the wood is dry.
  11. A method for drying wood in an unvented and insulated kiln using renewable energy as defined in claim 1, wherein the hot water filled air (17) enters a dehumidification device at the top of the kiln chamber (10) where the dehumidification device uses condensation to separate the water from the air and the water leaves the kiln (1), whilst the latent heat of condensation causes the air to cool, fall under gravity and the cool air (18) is returned to the base of the kiln chamber (10) to be reheated.
  12. A method for drying wood in an unvented and insulated kiln as described in claim 11, wherein the same air is reused throughout the drying process.
  13. A method for drying wood in an unvented and insulated kiln as described in claim 11 or claim 12, wherein the source of renewable energy is solar, wind, tidal or waste heat from an industrial process.
  14. A method for drying wood in an unvented and insulated kiln as described in any of claims 11 to 13, wherein the wood includes fine wood for cabinet making, wooden logs, wood chips or other forms of lumber.
  15. A method for drying wood in an unvented and insulated kiln as described in any of claims 11 to 14 using air circulation by natural convection currents and a passive gravity driven dehumidification device that has no moving parts and is not powered in any way

Description

WOOD KILN The. use of wood as a fuel source for heating is as old as the technology required to produce a spark to produce fire. Heating using wood is still common throughout much of the world, although it has been replaced with coal, oil or natural gas heating in most places. However, wood heating has been singled out as a serious health hazard in many regions of the world, despite the advances made in the devices in which wood combustion takes place. It is also now well known that most of these problems, such as smoke and particulate production, are caused by the moisture content found in the wood causing its incomplete combustion. Technology now exists to mitigate these problems and the moisture content can be reduced significantly. The invention discloses a method for drying wood or more precisely removing the water content from wood including fine wood for cabinet making and more specifically designs for a device for drying "green wood" in a novel design of wood kiln. One application is for drying firewood either in the form of logs, wood chips or other forms of lumber. This dry wood is burnt to provide heating, from small-scale domestic heating using wood-burning stoves, through to large-scale heating used by commercial users on an industrial scale. discloses how the use of wood as a fuel, particularly woodchips, is adversely affected by the water content of "green wood". Moisture content directly affects the calorific value of the wood as the water contained within the wood must be evaporated during combustion (the latent heat of evaporation). Therefore, the net calorific value of a fuel will decrease with increasing moisture content. Fuel with a higher moisture content also lowers the combustion temperature leading to incomplete combustion and increased emissions. This document also highlights that fuels, in this case wood, with a higher moisture content cost more to transport, as for any given volume of wood the weight will be higher as water is being transported too and therefore larger volumes of dryer wood can be transported in larger containers or at a higher bulk density. discusses the exploitation of biomass (wood) for energy production and the negative affect of high moisture content on the efficiency of power generation in combustion and gasification systems. This publication discusses different types of dryers and in particular rotary dryers for use in the drying process of woodchips. and granted versions PTL2, PTL3 relate to a solar powered drying, heating and air-conditioning system comprising an enclosure that defines a kiln chamber for drying a product, more particularly a charge of timber using air heated by solar radiation. However, the design of solar kiln described includes an "airflow system" using at least one fan for generating a forced, circulating airflow within the kiln chamber. describes a drying kiln where fresh air is added to the flow of circulating air. The drying kiln described has a horizontal floor that carries a heater battery and circulation fans and part of the circulating air in the kiln is vented from the kiln outside as exhaust airflow via an evacuation chimney. NPL3 teaches away from the conventional assumption that wood acts like a simple porous material, e.g. wet sand, when being dried. The surface of the sand becomes dry, and evaporation happens inside the pile as the 'Dry Front' moves deeper into the material. However, in this conventional model, vapour moves from the 'Dry Front' to the sand’s surface by diffusion as a vapour, it does not flow to the surface as a liquid, leading to the conclusion that using a faster airflow and/or converting a wood log into wood chips having a larger surface area to volume ratio will result in faster, more efficient drying, but this is not true. The model used for drying of simple porous material shows the drying rate decreasing as the 'Dry Front' moves deeper into the material and vapour diffusion becomes slower. However, with wood, results show that liquid water can flow from the middle of a log to the surface at a constant rate as it is wicked out along cell walls at the molecular level as discussed in NPL3 which explains how optimal drying conditions can be maintained if:“(i) Sufficiently wet conditions around the free surface of the sample are preserved, i.e., similar to those prevailing at the beginning of drying. (ii) Sufficient water is continuously transported towards the free surface to maintain these wet conditions.” The present invention provides a kiln that is unvented, relies on passive air circulation via natural convection, requiring no fan or similar means to provide a forced circulating airflow and uses passive gravity driven dehumidification. The wood is placed in a sealed kiln chamber with no ventilation, which is well insulated. This improves the efficiency of the heating system and results in a drying method that uses the minimum amount of energy during the drying process to achieve the maximum dryness