Cereals straw and agricultural residues for energy production in Latvia Msc. ing. Imants Plume, imants@sc.llu.lv Dr. Sc. ing. Dainis Viesturs, Latvia University of Agriculture, Latvia Latvia Habitants 2,3 milj. Area 64 600 km 2 Forests 45% Highest point above sea level 326 m Precipitation ~ 550...650 mm/year Evaporation ~ 400...450 mm/year Primaryenergyconsumption 199 PJ/year Share of renewable energy in primary energy consumption 34,5%
Renewable energy structure in Latvia (2004) Wood, straw biomass - 82.9% Hydropower - 16.4% Biogas - 0.42% Wind 0,28% Wood biomass for energy in Latvia (2004) Share of wood biomass in primary energy consumption 28,8 % Share of wood biomass for distric heating 24,2 % Share of wood biomass for local and household heating 56,2 % Utilized forest biomass (for different purposes) 10,75 milj. m 3 (78 PJ) Exported wood biomass 1,4 milj.t (25,2 PJ) Yearly growth of forest biomass -16,5 milj. m 3 (120 PJ) Potential for increase of wood biomass harvest for energy production 5,8 milj. m 3 /year (41,8 PJ)
Biofuel production for transport in Latvia Share of biodiesel and bioethanol in total fuel consumption for transport was 0,33 % in year 2005 (appointed 5,75% for Latvia in 2010). Produced Biodiesel from 62 000 tons of rapeseed (51 % of all rapeseed yield) in 3 plants and produced biooil in 1 plant in 2006. Produced Bioethanol from grain (wheat, rye, triticale) 9000 tons in 2006 (full capacity of 2 plants for bioethanol production was 19 500 t in 2006). Plants for electric energy production from renewable sources (2005) Hydropower plants produces 97,7% of all renewable electricity Cogeneration using wood 4 plants (2,5 MW) Cogeneration using biogas 3 plants (7,5 MW) The task for Latvia in producing of electricity from renewable sources is 49,3% of total electric energy consumption in 2010.
Agricultural areas in Latvia (2006) Agricultural lands in Latvia (2006) Area, thous. Ha 600 512 500 400 300 200 85 100 13 13 3 0 Cereals Rape legumes Sugar-beet Fodder-root Potato 441 346 250 45 13 2 3 5 Vegetable Other crop Green forage Green manure Nectar-crop Fallow (mowed grass) Unused (former agric.land) Cereals, rape straw and grass outcome in 2002-2005 Cereals and rape Area, th. ha (aver. 2002-06) Grain yield (aver. 2002-06), t/ha Grain:straw ratio Straw, grass, th. t Straw, grass, available for energy, th.t Wheat 215 3,1 ~1:0,9 600 Barley 136 2,1 ~1:1 285 Rye 43 2,3 ~1:1,2 118 Oat 53 1,7 ~1:1,1 105 Rape 51 1,7 ~1:1,3 114 Sum, straw 545 1216 174 (14 %) Fallow grass 341 1,9 649 325 (50% area)
Potential energy from agricultural biomass residues in Latvia (2006) Name of residues Straw Energy crop (maize, 2% of agr. land) Grass, fallow land Biomass Th. t 174 (18% moisture) 160 (DM) 325 (DM) Energy from burning PJ 2,5 2,1 (pellets) 4,5 (pellets) Biogas available Milj. m 3 22,4 (from maize juice) 48 (from grass juice) Biogas energy Livestock wastes 6100 (natural) Degradable 400 (natural) household wastes 290 6,5 2 Wastewater 180 (natural) sludge PJ 0,5 1,1 Energy from technically most feasible utilisation PJ 2,5 2,6 (2,1+0,5) 5,6 (4,5+1,1) Plant for straw burning in Saulaine, Latvia
Plant for heat energy production from straw in Saulaine, Latvia Power of plant for burning of 1,36 MW Efficiency of straw boiler 87% Efficiency of boiler together with distribution net 70% Heat energy produced 20 TJ/year Utilised biomass - wheat straw, 1300 tons/year Area for straw production 500 ha Average transport distance 6 km Density of square bales 0,11...0,12 t/m 3 Weight of bale 500 kg Straw price (transport costs included) 23,8 /t Investments 425 000 /MW Time of service of 20 years Running expenses, per year: Salary (for 4 persons) 47 000 /MW Refund of investments - 2150 /MW Purchase of straw - 23800 /MW Rate of interest 6% - 5750 /MW Electricity and materials 1550 /MW Overhead expenses-7000 /MW Total cost for 1 GJ energy production by straw boiler: 4,4 /GJ Calculation of amount of cereals and rape straw for energy in Latvia (2002-06) Cereals and rape straw available for energy calculates: S e = Y g -S m A s L M[t] where, S e straw available for energy, th. t; Y g straw yield, th. t; A - area of cereals and rape, ha; S m straw not removed from field to keep organic matter content at the same level for Latvia conditions, th. t, S m =1,6 t/ha; L straw for litter, t, I straw for chemical industry, t Amount of cereals and rape straw can be utilised for energy production (calculation was provided for 5-year period 2002-2006): S e = 1216-545 x 1,6 160 10 = 174 [th.t]
Constraints and recommendations for straw burning for energy Straw have significant content of Cl (Cl=0,17...0,6%), that may cause formation of dioxines at burning temperatures around 600 C, especially within lasting time of burning process. Straw contains significant content of N (N=0,5...1,2%), that can be a source of gaseous nitric oxides emission at temperatures above 750 C. Straw contains significant content of potassium, that facilitates melting of ashes at temperatures above 800 C. Recommendations An optimal burning temperatures of the straw are within range 700-750 C. Preferred is material supply in continuosly flow, that substantially decreases the time of exposing of straw at temperature 600 C, that prevent the formation of dioxines. Conclusions Potential of unharvested wood biomass energy in Latvia is 5,8 milj. m 3 /year (41,8 PJ/year). Potential of cereals and rape straw for energy production by straw burning is 14% or 174 thous. t/year (2,5 PJ). Potential of energy crop (maize) from 2% of argric. land (5,7 t DM/ha) for energy production is (2,6 PJ), that can be obtained by maize juice anaerobic treatment (0,5 PJ) and from pellets (2,1 PJ) produce from rest material. Potential of fallow grass (1,9 t DM/ha) by grass juice anaerobic treatment (1,1 PJ) and from produced pellets (4,5 PJ). Feasible biogas production potential is 30% or 2 PJ of theoretical biogas energy obtainable from animal wastes, degradable household wastes and wastewater sludge. Straw burning plant in Saulaine (Latvia) produces heat energy in price of 4,34 /GJ. It is recommended to feed boilers with straw in continuous flow and to keep process temperature in range 700-750 C to minimise excess dioxins or nitrite oksides formation as well as to prevent melting of ashes.
Thanks for attention