Evaluation of possibilities growing and using tall perennial grasses for fuel

Abstract

The combustion temperature of the biomass of swards cut in the late summer or early spring was the highest and had the lowest NOx content in flue gases. The mass of reed canary grass and its mixtures with goat's rue burned the best. In Lithuanian climatic conditions the energy potential of tall-growing grass swards cultivated on light soils low in humus content was 115-153 GJ ha-1, and energy input for biofuell production amounted to 8.0-19.2 GJ ha-1. The present paper provides the results of the tests on tall-growing perennial grass biomass suitability for use as fuel, as well as the findings on energy potential of swards and energy efficiency of biofuel production from herbaceous plants. The tests were conducted for three years. Eight swards differing in species composition were grown. Two of them consisted of pure rhizomatous grasses - reed canary grass (Phalaris arundinacea L.) and awnless bromegrass (Bromus inermis Leyser.), treated with mineral fertilizers, applying N60 split in two applications. The other swards consisted of the above-mentioned grass mixtures with legumes-sweet clover (Melilotus officinalis Lam.), perennial lupine (Lupinus polyphyllus Lindl.) and goat's rue (Galega orientalis Lam.). The mixtures did not receive nitrogen fertilizers. The soil of the experimental site is light loam with a humus content of 1.5-1.9%. The swards were cut in June, July, August, September and March and were analysed for dry matter (DM) yield, fibre content in DM, calorific value and combustion temperature of biomass, and NOx content in smoke when burning the biomass in the heart-type furnace. Energy potential of swards and energy input for biofuel production were calculated according to the DM data. The productivity of swards under congenial wheather conditions ranged between 6.3-8.8 t DM ha-1, while under adverse conditions between 2.8-6.5 t ha-1. The swards of reed canary grass and its mixtures with perennial lupine and goat's rue were found to be more productive. Fibre content in DM was highly depended on the cutting date of swards, i.e. on the maturity of swards at harvesting and fluctuated from 38 to 45%. The net calorific value of dry biomass ranged from 17.1 to 18.5 MJ kg-1 and depended on sward composition, growing conditions and cutting time. Combustion temperature ranged from 770 to 951°C.