Renewables
Ten tons of Alamo switchgrass (Panicum virgatum) could dramatically change the way utilities produce electric power. A research project, that is involving Southern Research, Southern Company, Auburn University, the Electric Power Research Institute (EPRI), the Alabama Department of Economic and Community Affairs (ADECA), and the US Department of Energy (DOE), is currently being carried out in order to study ways in which switchgrass can be grown, harvested and blended with coal for use as a fuel for power generation.
Southern Company is attempting to blend coal with biomass sources – such as switchgrass. If successful, the project could result in emission reductions from the coal-fired power plants.
To determine the effectiveness of this, a pilot-scale power plant located on Southern Research’s Southside campus is being set up. This is due to commence operation this month, and the testing will last for 14 months. First indications of results should be available in late Spring 1999. This will give a clear indication of what the likely results will be. The tests will evaluate the optimum coal/switchgrass blend ratio, effects on corrosion and fouling rates, and the effect on emission level reduction.
The switchgrass will be pulverised and blended with varying amounts of coal to determine the most effective mixture. Mixtures of 5, 10, 15 and 20 per cent of switchgrass are being tested. The pilot plant will test the crushing, pulverisation, and combustion of coal and switchgrass. Two different types of coal will be used in the test: one will be hard, bituminous coal from the Appalachian mountains, the other being a low-rank soft coal from Wyoming.
In addition, the pilot project will test the effect of the pulverising action of the coal on the switchgrass. This will have an effect on the ease and cost of co-milling and co-pulverisation.
Dr David Bransby of Auburn University’s Agronomy and Soils Department said that the blend reduced emissions of NOx and SOx. SOx reduction is a dilution effect, while the NOx reduction results from the changing properties of the flame dynamics.
“Mixing switchgrass with coal is both effective and economically promising, because it doesn’t require any changes in existing technology at power plants,” said Charles McCrary, president of Southern Company’s generation business unit. “Instead of retrofitting plants, which would ultimately result in higher costs to the consumer, we are working with scientists at Southern Research and Auburn University to change the fuel blend. It’s a novel approach, and if it works, there’s potential for immediate commercial use.”
Mr Vann Bush, manager of the Emissions Control Group of Southern Research Institute, said that the cost of the mixture would inevitably be greater than the cost of coal alone.
In addition to reducing NOx and SOx emissions, the use of switchgrass will reduce the release of CO2 into the atmosphere. Switchgrass removes CO2 from the atmosphere, and incorporates it into plant tissue. This accumulation of carbon is known as carbon sequestration, and is a very important strategy for reducing atmospheric CO2. When switchgrass is burnt, it releases the stored carbon into the atmosphere as CO2, making it CO2 neutral.
“It’s important that we support the development of energy sources that prove to be both cost-effective and environmentally friendly,” said US Senator Jeff Sessions. “Switchgrass has great promise as a fuel, as well as being a potential cash crop. This project holds a great deal of promise not only for Alabama, but also for the entire nation.”
According to Dr Bransby, it takes approximately 3 years for production of switchgrass to reach an optimum level; it produces a third yield in the first year, about two thirds in the second, and only reaches full yield in the third. About 800 acres of farmland is required to provide switchgrass to fuel 1 MWe.
Southern Company has provided 30 per cent of the funding for the $2.2 million research project. The other private partners provided 25 per cent, with the remainder being provided by the US Department of Energy.
A full scale test is planned to be undertaken in the Autumn of 1999 at the Gadsen Steam Power Plant in Gadsen, Alabama. This plant consists of two 60 MWe steam turbines, and the test is scheduled to last for three weeks.