Biomass or biomess?

I wrote the article below for the Building Services Journal, who have kindly allowed me to reproduce it here.

Biomass is on everyone’s list of an environmentally friendly and sustainable energy sources, even though it involves burning fuel.  Many developers these days have to comply with the Merton Rule, whether they are environmentalists or not. This requires a percentage of the energy used by a new development to be generated on site.

In developments everywhere, developers and local authorities working together believe that the way to comply with the sustainable on site generation required by the Merton Rule happens also to be the cheapest way – installing a biomass boiler. The theory goes that when you burn biomass to create heat all you are doing is accelerating the release of carbon that would happen if the biomass were left to decay. I am not so sure.

I know that burning biomass immediately releases carbon dioxide in huge quantities whereas leaving it to rot releases most (but not all) carbon dioxide much more slowly. Some rotting substances, particularly in unmanaged woodlands or wetlands, decay into peat, locking up much of their carbon dioxide until released by burning. Sometimes it is never released by burning. 

Also, I am not convinced replanting is on a scale capable of soaking up all the carbon dioxide released by burning. Burning biomass releases the carbon that the plants absorbed in growing; if you cut down a mature forest and burn it, you have to replant on a scale to ensure that you soak up all the carbon that you released, including the carbon used in transporting the biomass around.  

The carbon cycle is not completely closed when burning biomass. The biomass industry estimates the carbon that is not recycled to be around 5% of that released by burning, but I suspect that is an optimistic figure. Most biomass boilers in this country use wood pellets. The fear of a supply problem with pellets often results in many developments having a gas boiler as back-up, although I suspect that in many cases the gas boiler ends up being more than just a back-up. 

While there is a case for biomass it is not always the best way of providing environmentally friendly benign energy. Burning wood pellets is not benign. When you burn wood you release wood smoke, which contains inorganic gases such as carbon monoxide but also organic gases, particulates, and organic compounds (such as benzopyrenes) which are carcinogens. 

True, most of the gases, particulates and compounds can be filtered out of the smoke before it reaches the flue. But efficient filtering depends on a rigorous and effective maintenance program; we know from our experience with gas boilers that these are not always in place. And however good the filtration, there will always be some leakage to the atmosphere. 

Maintenance is very important with all burning devices. For biomass boilers it must include not only checking the flue and filtering system but also the regular cleaning out of wood ash. Although wood ash can be recycled into fertiliser, in places where wood combustion is very high, Finland and Sweden, less than 10% of wood ash is recycled and more than 90% of wood ash is put into landfill sites.

The reason for this is that in order to spread wood ash in a safe way, because of the health risks, the ash has to be compacted and granulated. And also because some wood ash contains cadmium and other heavy metals, it will poison instead of fertilise.  

Let us assume, then, that the biomass wood burning boilers all have good working filters will that be enough? Wood smoke created by the boilers is designed to be sent through a flue into the atmosphere. The filter will let through wood smoke particles unless it has a very expensive system of smoke washing. When you breathe them in these particles are too small to be filtered by the nose or the upper respiratory system so, like tobacco smoke, they will end up deep in the lungs.  

In addition, if wood smoke is inhaled many common conditions, such as asthma, bronchitis and emphysema may be aggravated, or in the long term created. Researchers at the United States Environmental Protection Agency suggest that lifetime cancer risk from wood stove emissions may be 12 times greater than the risks from exposure to an equal amount of cigarette smoke. However, I am not aware of any research conducted into the effects of breathing burnt wood pellets created by a biomass boiler 

There are technologies that we should use before biomass; thermal solar and geothermal energy as well as wind energy are all benign; each of them has different carbon paybacks but with most thermal solar systems the carbon used in manufacturing, transporting and installing is recovered in less than two years, as opposed to the attempted closed carbon cycle of a biomass system. Let us hope that the biomass lobby does not convince Mr Wicks that this is the only way to secure our crabon emission reductions, otherwise we may see a return to the bad old pre clean air legislation days.