2003 Council on Forest Engineering (COFE) Conference Proceedings: Forest Operations Among Competing Forest Uses Bar Harbor, September 7-10, 2003

Transcription

1 CO 2 FIXATION IN POPLAR I-214 PLANTATIONS AIMED AT ENERGY PRODUCTION Francisco Marcos-Martín 1, Fernando García-Robredo 1, Inés Izquierdo-Osado 1 and Santiago Villegas-Ortiz de la Torre 2 1 Escuela Técnica Superior de Ingenieros de Montes. Universidad Politécnica de Madrid. 2 Escuela Universitaria de Ingeniería Técnica Forestal. Universidad Politécnica de Madrid. Ciudad Universitaria s/n, E Madrid, SPAIN fmarcos@montes.upm.es ABSTRACT CO 2 fixed in two year rotation plantations of poplar I-214 for energy production is studied. The experimental site is located in Cabrerizos (Salamanca). Estimated productivity ranged from 18 to 26 odt/(ha yr). The results obtained for the lowest estimate (18 odt/(ha yr)) show that CO 2 fixed reaches 5,992 kg/ha and kg/kwh produced. INTRODUCTION The Plan for the Development of Renewable Energy Sources in Spain (IDAE, 2000), passed by a Ministers Council on December 30 th 1999, stresses on the so called ligneous crops as an energy source. The growing of I-214 is one of the crops to consider. In other countries willow trees (Labrecque et al. 1995, 1998) and other hardwood plantations (Stokes, 1993; McDonald and Stokes, 1994) are used. In addition, the Kyoto protocol in 1997 intended to implement some measures so that the atmospheric CO 2 was fixed to the ground rather than ascending continuously to the atmosphere when fossil fuels are burned. OBJECTIVES The objective of this communication is to determine the amount of CO 2 fixed by the energy crop. In order to accomplish this objective, the methodology developed by Fernández (1998) and Lewandowski (oral communication) has been followed. This methodology has been modified by Marcos et al. (2000) and has been adjusted according to the data provided in the literature and consultations to experts. The experimental site is located in Cabrerizos (Salamanca) where a two year rotation crop for energy production with a density of 33,333 plants per hectare has been established (Marcos et al, 2002).

2 METHODOLOGY The estimates of CO 2 fixed per electric kwh produced will be calculated on the assumption that the I-214 biomass is transported to a thermal power plant where it is burned to produce electric energy. Two stages can be identified in the calculation process: Stage A: Growing + transportation to a thermal power plant. - Dry matter production (odt/(ha yr)). Following publications by San Miguel and Montoya (1984) and San Miguel et al. (1992), an initial production of 18 odt/(ha yr) will be assumed. - Amount of carbon per ton of dry matter: The figure of 500 kg (that is, 50%) will be considered based on the average data used by Marcos et al. (2000) after a thorough bibliographic review. Rueda (1997) also assumes a carbon percentage of 50% for Populus tremula. - CO 2 fixation: Similarly to other agroenergy species (Fernández, 1997), it can be assumed that 1.25 grams of carbon are fixed per gram of carbon fixed in the wood. The remaining 0.25 is the amount fixed in the mineralization process, the floor humus and the roots attached to the stump. In this kind of crop, the stems are cut every two years along a six to eight year cycle. At the end of the 3 rd or the 4 th cut, the stumps must be crushed and incorporated to the ground. - CO 2 emission: According to Fernández (1997), a total value of 0.77 tons of CO 2 per hectare and year are sent to the atmosphere as a result of the planting, fertilizing, maintenance, weed and pest control operations carried out in crops of thistle (Cynara cardunculus). This figure comes from the contribution of machinery (0.25 t), raw material including seeds, fertilizers, herbicides and pesticides (0.46 t), and biomass transportation to the power plant (0.06 t). In the case of poplar I-214, an accurate calculation should be done, but initial estimates in Spain and Chile have given values around 0.77 t. Irrigation has been considered at the end of the calculations as a reduction factor, since it strongly depends on the area where the I-214 plantation is carried out. The reference datum for irrigation is 76 grams of CO 2 per each MJ used in water pumping. Stage B: Combustion and electrical energy generation. - Anhidrous high heat value: A value of 4,200 kcal/kg = 17,556 kj/kg has been considered. Following Gimeno (1989), the values of the high heat value for the wood of Populus nigra L range from 4,449 kcal/kg (Fabricius and Gross) to 4,601 kcal/kg (Feher), therefore the value of 4,200 kcal/kg seems acceptable according to published results of a series of laboratory analyses (Elvira and Hernando Lara (1989)) and the expected value taking into account the I-214 wood chemical composition.

3 - Thermal plant working hours: The value of 6,750 hours/year has been selected according to data from the Spanish Atomic Forum and the International Energy Agency (IEA). - Energy efficiency in terms of electrical energy is calculated as the quotient between the number of electric kilowatt-hour (kwh) and the product of the mass by the reference heat value of the proposed plant, and is equal to 30% because of the good combustion characteristics of the poplar wood. The ashes and the solid particles obtained in the combustion process are recycled in the same plantation site, thus closing the nutrient cycle. - The unit conversion is given by: 1 electric MJ = electric kwh. - Drying: It has been estimated that 3% of the available energy is spent in the drying process. Natural drying and a countercurrent drying place are used for that purpose. The methodology used in the research is summarized in a flowchart as follows: TWIG PRODUCTION LAND DEVELOPMENT PLANT-KILLING AND INSECTICIDE PRODUCTION TRANSPORT OF TWIGS PLANT-KILLING AND INSECTICIDE UTILIZATION TRANSPORT OF FITOCIDE, INSECTICIDE PLANTATION 1 st year WEED CONTROL 1 st year IRRIGATION FITOCIDE, INSECTICIDE PRODUCTION FITO/INSECTICIDE UTILIZATION FITOCIDE, INSECTICIDE TRANSPORT 2 nd YEAR IRRIGATION HARVESTING

4 CO 2 fixed/ kwh RESULTS Balance of CO 2 fixed: Since the CO 2 gram molecule weighs 44 g and contains 12 g of carbon, the amount of CO 2 fixed (FI) may be calculated as FI = 18,000 kg 0.5 (44/12) 1.25 = 41,250 kg = t of CO 2. The CO 2 emission during Stage A, growing + transportation, (E1) is equal to 0.77 t of CO 2. The amount of CO 2 emitted during the combustion process (E2) is given by: E2 = 18,000 kg 0.5 (44/12) = t of CO 2 /ha The balance of CO 2 fixed per hectare (BA) is calculated as: BA = FI E1 E2 = = 7,490 kg CO 2 /ha. Electrical energy production: The electrical energy obtained is given by: 18,000 kg 17,556 kj/kg 0.3 = 94,802.4 MJ kwh/mj = 26, electric kwh Since 3% of the energy produced is spent in the drying process, the available energy (PE) is equal to PE = 26, kwh 0.97 = 25, kwh e. The installed power can be obtained in the following way 25, kwh / 6,750 h = 3.78 kw. The balance of CO 2 fixed in relation to the electrical energy produced (BAE) is given by: BAE = BA/PE = 7,490 kg / 25, kwh = g/kwh This figure is above the 214 g/kwh quoted for the thistle crops (Fernández, 1997), but it must be recalled that in this work two main assumptions have been made: there is enough water for irrigation and a dry matter production of 18,000 kg/(ha yr) is attained. Assuming that 76 grams of CO 2 are emitted per MJ of energy used in water pumping, the latter values are cut down by 20%, that is BA = 5,992 kg of CO 2 fixed per hectare, BAE = g of CO 2 fixed per electric kwh produced.this value is still slightly higher than the figure of 214 g/kwh obtained by Fernández (1997) in thistle crops. The relationship between biomass yield and CO 2 fixed is shown as follows: CO 2 fixed / kwhe 15,00 12,00 9,00 6,00 CO 2 fixed in SRC of poplars t de CO2 fijado/ha-año kg CO2 fijado/ kwhe 5,55 5,50 5,45 5,40 5,35 5,30 5, , Productivity (t dm /(ha-year)) Productivity (t dm/(ha-year))

5 REFERENCES Elvira, L. y C. Hernando-Lara Inflamabilidad y energía de las especies del sotobosque. INIA. Madrid. Fernández González, J La biomasa como energía alternativa para reducir el CO 2 atmosférico. Homenaje a D. Angel Ramos Fernández. pp E.T.S. de Ingenieros de Montes. Real Academia de Ciencias Exactas, Físicas y Naturales. Academia de Ingeniería. Madrid. Gimeno, C Poderes caloríficos de especies forestales españolas. Tesis Doctoral. Madrid. Labrecque, M., T. I. Teodorescu and S. Daigle Effect of wastewater sludge on growth and heavy metal bioaccumulation in two Salix species. Plant and Soil. 171: Labrecque, M., T. I. Teodorescu and S. Daigle Early performance and nutrition of two willow species in short-rotation intensive culture fertilized with wastewater sludge and impact on the soil characteristics. Canadian Joural of Forest Research. 28: Instituto para la Diversificación y Ahorro de la Energía Plan de Fomento de las Energías Renovables en España. IDAE - Ministerio de Industria. Madrid. Marcos Martín, F., I. Izquierdo Osado and J. Ruiz Castellano Cultivos energéticos de chopos. Revista Forestal Española. 26:4-14. Madrid. Marcos Martín, F Biocombustibles sólidos de origen forestal. AENOR. Madrid. Marcos Martín, F., S. Villegas Ortiz de la Torre, F. García Robredo, I. Izquierdo Osado and J. Ruiz Castellano Two year - rotation plantations of poplar trees for energy. Proceedings of the 25 th Annual Meeting of the Council on Forest Engineering. Auburn, Alabama. McDonald T. P. and B. J. Stokes Harvesting Costs and Utilization of Hardwood Plantations. Proceedings of the IEA/BA Task IX, Activity 1. USDA Forest Service. Auburn. Alabama. Rueda, J La madera de chopo y sus aplicaciones. Junta de Castilla y León. Valladolid. San Miguel Ayanz, A. and J. M. Montoya Resultado de los cinco primeros años de producción de tallares de chopo en rotación corta (2-5 años). Anales del Instituto Nacional de Investigaciones Agrarias. Serie: Forestal. 8: Madrid. San Miguel Ayanz, A., J. San Miguel Ayanz and S. Yagüe Tallares de chopo a turno corto. 19ª Sesión de la Comisión Internacional del Álamo. Zaragoza.

6 Stokes, B and Bruce R. Hartsough Development and analysis of SRIC harvesting systems. In. Proc. First Biomass Conference of the Americas, 1993; August 30- September 2. Burlington VT. National Renewable Energy Laboratory, Golden, CO