Chapter 5.
SAFETY PRECAUTIONS AND ENVIRONMENTAL CONSIDERATIONS.
5.1 SAFETY PRECAUTIONS IN CHARCOAL OPERATIONS.
“Whether charcoal is made in the traditional way or by industrial methods, three hazards are always present:
1. Fire of stored charcoal.
2. Gas and dust explosions
3. carbon monoxide poisoning.
5.2 EXPLOSIONS
“The admittance of air can form highly explosive gas mixtures and may cause first a sudden rise in temperature and then formation of explosive mixtures in the off-gas system”
5.3 FIRES
“Fire can result from admission of large amounts of air through cracks or badly closed doors in other cases fire can result from explosions caused by operators simple carelessness. The inflow of excessive amount of air can change the temperature pattern creating a serious fire condition.
SAFETY DEVICES AND EQUIPMENT.
5.5.1 PRESSURE RELIEF DOORS.
Explosions are always possible when handling a dusty material or one which contains combustible gases and vapours. Thus, the feed and storage bins are designed with explosion blow out panels which vent gases when the internal pressure goes above 350 – 400mm water.
5.6 PRECAUTIONS FOR CHARCOAL STORING.
A great deal of care must be taken when storing freshly produced charcoal. It has a tendency to absorb the oxygen from the air. Rapid absorption creates considerable heat, which builds up to a point where the stockpiled char will start burning. Self ignition may even occur if charcoal has been water sprayed for better cooling.
5.7.1 WATER SUPPLY.
A water supply is highly important to any charcoal plant. A hose with a nozzle should be kept ready for immediate use at assigned points of the plant. Back pack water pumps or large capacity fire extinguishers provide some measure of fire protection.
5.8.1 GENERAL CONSIDERATIONS.
The environmental aspects of industrial charcoal making depend very much on the type of system and the type of raw material. In general, the most important problems are odour and dust. the others can be eliminated.
5.8.2 RAW MATERIAL PREPARATION.
Logging machinery is usually noisy and may exceed local decibel allowances. It is good practice from all points of view to local carbonisation plants at least 1km from residential areas and preferably down wind of them to avoid odour, dust and noise pollution.
5.8.4. CHAR HANDLING
Conveyer belts are normally enclosed to prevent wind scattering dust. The fumes of dust from the char hoppers are drawn by exhaust fans through bag filters which capture the dust. The dust is periodically shaken from the bags into the collecting bins attached. But disposing of the fine dust is a problem unless it can be mixed to the feedstock of a briquetting plant.
5.8.5 RETORT CONDENSATES AND GAS.
The direct loss of gas and vapour from retorts must be avoided as much as possible to prevent direct air pollution.. The condensates are difficult to dispose of, the simplest way is to burn them off as they emerge as hot gas from the retort before they condense. Where small amounts of condensate arise they can be collected in ponds and subsequently burnt after the water they contain has largely evaporated. This can prove impossible however in areas of high rainfall.
Retorting systems are designed so that in the case of an unusual pressure rise within the system as may result from a fire the vapours are vented into the atmosphere. This is done for safety of personnel and equipment. since the venting is to the open air, the vapours quickly disperse.
5.8.6 WATER WASTE
The control and discharge of waste water from carbonisation plants is of the highest importance as untreated waste water can be a serious environmental pollutant in streams used for drinking, stock watering and fishery.
The problem with condensed water in the complex technology plant is that it is usually contaminated with acids and tars condensed from the retorts off gases and hence cannot be allowed to escape into streams without treatment.
The waste water can be accumulated in settling ponds and allowed to evaporate. The tarry residues remaining are periodically burned off.
6.9.2 PYROLIGNEOUS ACID
Pyroligneous acid is the name of the crude condensate and consists mainly of water. It is highly polluting noxious corrosive liquid which must be either worked up properly to produce by products for dale or burned with the help of other fuel such as wood or wood gas to dispose of it.
The non-water component consists of wood tars, both water soluble and insoluble, acetic acid, methanol, acetone and other complex chemicals. If left to stand the pyroligneous acid separates into 2 layers comprising the water soluble tar and a watery layer containing the remaining chemicals.
One ton of dry wood produces about 40kg of tar. i.e.. about 4% yield.
The water layer contains water soluble tars which are complex tarry chemicals, acetic acid, methanol, acetone and methyl acetone and small amounts of more complex acids and other substances.
