Good reliable fuel supply for Biomass Boilers

EC Drummond's Wood pile

The future for poultry growers

The future for poultry growers

Sourcing a good reliable fuel supply is top of the ‘must have’ list for anybody running a biomass boiler and, as time goes by and more people take-up the RHI, more and more fuel supply companies are springing up. My inbox is full of contacts from all over the country who find us by various means and want us to pass their details on to our customers.

I generally ask them a few questions about what they supply, what the water content is, whether they do a biomass fuel supply contract paid on the meter (most don’t), whether there is any recycled material mixed-in and if so what the source of that material is.

One of our ETA Poultry Team partners had a great deal of trouble with one source of recycled fuel his client bought. It was chipped-up cable drums. You sometimes see these huge wooden bobbins mounted on trailers by the roadside when electrical companies have large quantities of very big cable to install. Apparently the drums cannot be re-used (another case of health and safety gone mad), so they end up surplus to requirements when they are still ostensibly perfect.

The problem was that the wood was so old and so dry and so light that it wouldn’t fall into the open auger trough any sense, and even when they got enough into the screw to burn it had very little calorific value. This is why you shouldn’t keep your logs too long as well — the longer you keep them, the more calorific value they lose.

I spoke to one supplier last week, who said they output virgin timber at an average of 30% moisture. Could be 30%, could be 35%, may be higher or lower than that. They don’t dry the chip at all to give a consistent product — you just get it as it comes. I was thinking this type of supplier will gradually fade away, because those suppliers who have invested in the infrastructure to dry chip to a consistent moisture level will capture the market. It seemed pretty obvious to me that people would prefer to know exactly what they were getting every time, and would buy accordingly.

EC Drummond's Wood pile

EC Drummond’s Wood pile

Makes sense, but this is not what is happening. People are buying wood chip with 50% moisture content in preference to chip at 20% moisture content (perfect), because they think the wetter chip is cheaper at £50 per tonne than the dry stuff at £90 per tonne.

With 50% moisture at £50 you are paying £25 for half a tonne (500kg) of water, and £25 for half a tonne of wood. With 20% moisture at £90 you are paying  £18 for 200kg of water and £72 for 800kg of wood, so your price per kilo of wood is £0.09 with 20% chip and £0.05 per kilo of 50% chip. So on first look it does seem to be cheaper to buy wet wood.

It is, but only if you dry it before you burn it. If you put wet chip into a boiler and burn it, several things happen. You can’t burn water, obviously, so when you introduce wet chip into the burning chamber it will not ignite until some of that moisture has been boiled off. Boiling the water off takes energy in the form of heat, which reduces the heat output of the boiler. Tar is produced, which coats and insulates the heat exchanger surfaces of the inside of the boiler, which further reduces its output. The tar coats and fouls the lambda probe, which is there to govern the efficiency of the burn by measuring the oxygen levels in the flue gases. If it gets clogged-up it can’t do its job.

This is the same in every make of boiler, regardless of what claims are made by salesmen.

The ideal scenario, if you are not chipping your own wood, is to buy fuel on the basis of a per KW reading on your heat meter. The only fuel suppliers who offer this service at a reasonable rate are those who have complete confidence in the quality of the fuel they supply. A salesman for a rival company using a different boiler to us has been claiming he can get a fuel supply contract for his boilers with Eddie Stobart Biomass at 2.1p per KW. Of course we had to find out if this was true, because it seemed too good, so we rang Stobarts and talked to the guy in charge of biomass meter contracts. He said they offer in the range of 2.6p – 3.2p depending on the meter calibration, service contract and a 3 months trial on tonnages used, and the meter reading to establish the final rate. There is no preferencial treatment given to any make of boiler, and a 2.1p rate has never been, and will never be offered to anybody, as it is lower than the cost of production.