Introduction to the Advantages and Disadvantages of Switchgrass as Biomass
Switchgrass is widely cultivated in the US both as a soil restoration crop and a biomass crop, being easily harvested using proven techniques. It is usually transported in large bales to the nearest facility where it is used to produce liquid or solid biomass fuel, both considered as a source of renewable energy.
This is an article on renewable energy, and in particular the pros and cons of using Switchgrass as a biomass fuel when used as a fuel along with pulverized coal in a co-fired thermal power plant. We begin with an overview of a typical co-fired power plant.
Overview of a Co-fired Power Plant.
Co-fired power plants using biomass such as switchgrass along with coal are becoming a more popular means of producing electricity with reduced harmful emissions to the atmosphere.
Below is a sketch of a typical co-fired thermal power plant where the switchgrass can contribute up to 20% of the fuel, the other 80% being coal.
Switchgrass is harvested using traditional agricultural crop harvesting machinery, about 6" of the stalk being left above the ground. The switchgrass is transported to the facility in large rectangular bales (3’x 4’x 8’) weighing 1000lbs, where they are loaded onto the process supply conveyor. The bales are passed through a de-stringer / de-baler and under an electromagnet, preparing the biomass for the next process. Here it enters a hammer mill where the switchgrass is ground into thin, two inch long strips, much resembling a matchstick. From the hammer mill the crushed particles are blown through cyclones and bag filters that remove the dust and smaller particles.
The resultant particles are then blown through pipework into the furnace burners of a water-tube boiler. Here they ignite and supplement the coal burners in supplying superheated steam to the turbines that drive power generators.
Reference Web: Co-fired Power Plants
Advantages and Disadvantages of Switchgrass as Biomass
The cultivation of switchgrass by farmers in America as a biomass for fuel is increasing; however there are advantages and disadvantages in the processing of switchgrass as listed below:
1. Cultivation and Harvesting of Switchgrass.
- Can grow in drought or very wet conditions.
- Can grow in soil of poor condition.
- Can improve the condition of poor soil.
- Ability to produce high yields with little use of fertilizer/herbicides.
- Does not require replanting every year, the original plants can last as long as 20 years.
2. Can be processed to produce liquid fuel or solid fuel for the domestic or industrial markets.
3. Classed as renewable energy source with zero carbon emissions.
1. Switchgrass biomass contains sulfur, so when combusted the fumes if not treated can emit SO2 to the atmosphere causing acid rain. The fumes also contain particulates that are very harmful to the breathing system if inhaled.
2. Some power plants using switchgrass as a co-firing fuel have had complaints from locals on air quality/emission standards. Third world countries are especially guilty of emitting SO2 and particulates to the atmosphere
2. Harvested switchgrass is normally baled; these are large and weigh 1000lbs; being expensive to transport these also require stored under cover and clear of the ground.
3. The ground used to cultivate switchgrass could be used to grow food – ongoing debate regarding food or fuel.