Wood energy

This Technical Guide provides guidance on the conversion of existing coal fired boilers to wood pellet operation. There are a number of obvious advantages to using wood pellets: they are 100% renewable and relatively clean burning. Of paramount importance in a conversion is the need both to maintain the safety and integrity of the boiler and control systems, and also to improve safety to the level of best practice.

Pacific Wood Products (PWP) installed Ecogate control systems on their extraction fans. Through the use of air flow control gates and a variable speed drive connected to each fan that adjusts to meet the actual workload, PWP reduced their energy use substantially.

Energy savings were immediate from week one. The system will be paid for in be just over 4 years, and long-term they benefit from lower energy bills. Equally important, PWP will cut its annual CO2 emissions by 45 tonnes.

After a long period on the sidelines, gasification is attracting new interest.

For businesses with ready access to a good source of wood fuel - and increasingly other forms of biomass - it could be a very attractive way of producing low-cost and low-emission heat and electricity. This article overviews the technology and shares the experience of the ‘advance guard' driving this technology forward in New Zealand.

Waste was one of the first considerations for Southern Pine Products when it started manufacturing MDF (medium density fibreboard) products.

The company opted to install a briquette press, which turns MDF dust into combustible briquettes for boiler fuel.

Moffatts Flower Company, a greenhouse complex only 5 km from Southern Pine, now buys all the briquettes the company produces.

The saving in Southern Pine's waste disposal costs is projected to be $180,000 a year and annual revenue from briquettes is projected to be around $25,000.

A 50kW wood pellet-fired boiler is proving considerably cheaper than electricity for heating the Bay of Plenty‘s 30 bed Titoki Healing Centre.

Fully automated and fed by a 3-tonne hopper topped up by the truckload, the system operates virtually hands-free.

Installation cost around $80,000. That compared more than favourably to the other main option, heat pumps, at around $90,000. Running costs are even more competitive at about $4,400 annually, almost a third of the costs estimated for running heat pumps.

In May 2008 Cashmere High School switched from coal to renewable wood energy to heat its site.

The new boilers produce around five times less particulate emissions than a typical school coal boiler. Carbon emissions have reduced by 216 tonnes per year. The wood-fired system is also 14% more efficient.

"There used to be soot and ash in the gutters. Now we just have clean, clean emissions," says Cashmere High support services manager Roger O'Regan.

With its future at stake, New Zealand Foam Latex needed an economically viable and environmentally friendly fuel to produce steam needed to manufacture their products - all made from foam.

Coal was cheap, from $6.10/GJ. But emissions and the costs of mitigating them ruled it out. Diesel and LPG would cost over $30/GJ.

Wood was cost-effective and clean-burning. A variety of sources helped assure reliable supply - forestry hoggings, timberyard residues, left-over pallets and demolition, even dunnage reclaimed from shipping.