Obtaining of grass biomass for the production of solid fuel. Summary of the doctoral thesis for the scientific degree of Dr.agr. | Zālaugu biomasas ieguve cietā kurināmā ražošanai. Promocijas darba kopsavilkums Dr.agr. zinātniskā grāda iegūšanai

English. The research task was the impact of different nitrogen fertilizer norms on grass yields and the quality and bioenergy properties of different biomasses of grass species and timber and their mixtures used for the production of solid biofuel. Field tests were established at the LLU Study and Research farm “Pēterlauki” and included six grass species: festulolium (× Festulolium Asch. and Graebn.), cocksfoot grass (Dactylis glomerata L.), reed canary grass (Phalaris arundinacea (L.) Raush.), tall fescue (Festuca arundinacea Schreb.), meadow fescue (Festuca pratensis Huds.), and timothy (Phleum pratense L.). Seven nitrogen (N) fertilizer rates were compared: 0, 30, 60, 90, 120, 150, and 180 kg haE-1. Basic fertilizer was supplemented with phosphorus (80 kg haE-1 P2O5 – simple granular superphosphate) and potassium (120 kg haE-1 K2O – potassium chloride). The variant with no fertilizer was used as a control. For the formation of pellets, biomasses of five kinds of timber were used: birch (Betula pendula Roth.), osier (Salix spp.), grey alder (Alnus incana (L.) Moench), aspen (Populus tremula L.), and hybrid aspen (Populus tremuloides × Populus tremula). The dry timber powder used for research was obtained at the State Forest Research Institute “Silava” (located in Salaspils). The highest nitrogen fertilizer return from 1 kg of N was recorded for cocksfoot grass and meadow fescue applying nitrogen fertilizer norm of 30 kg haE-1, and for reed canary grass, timothy, tall fescue and festulolium applying 60 kg haE-1 N fertilizer norm. The amount of energy produced varied from 93.6 GJ haE-1 for meadow fescue to 112 GJ haE-1 for timothy. The highest amount of energy was produced when grass species biomass was mixed with osier in the proportion of 3/1 (75 % of timber + 25% of grasses), whereas the smallest amount of energy was obtained when grass species biomass was mixed with aspen. Phosphorus and potassium fertilizer (P80K120) increased the produced energy amount from 13% for tall fescue to 35% for meadow fescue, whereas the use of nitrogen fertilizer – from 21% for tall fescue to 53% for timothy. The highest gross calorific value was detected for timothy and for the biomass mixture in the proportion of 3/1: reed canary grass, festulolium and timothy mixed with birch or osier. The lowest energy cost was obtained from the biomass of reed canary grass, and the most expensive energy was from meadow fescue biomass. The research results demonstrated that energy cost price from the biomass of grass species was higher than that from the biomass of timber.

Latvian. Darbs izstrādāts LLU Mācību un pētījumu saimniecībā (MPS) „Pēterlauki”, kur 2011. gadā tika ierīkots lauka izmēģinājums ar sešām stiebrzāļu sugām: miežabrālis (Phalaris arundinaceae (L.) Raush.), auzeņairene (× Festulolium Asch. and Graebn.), timotiņš (Phleum pratense L.), pļavas auzene (Festuca pratensis Huds.), niedru auzene (Festuca arundinaceae Schreb.) un kamolzāle (Dactylis glometata L.). Tika ierīkoti šādi mēslojuma varianti: (1) N0P2O50K2O0 kg haE-1 – kontrole; (2) P2O580K2O120 kg haE-1 – pamatmēslojums (F); (3)–(8) pamatmēslojums ar sešām slāpekļa mēslojuma normām: 30, 60, 90, 120, 150 un 180 kg haE-1 N. Slāpekļa mēslojums bija amonija nitrāts (NH4NO3), fosfora mēslojums – vienkāršais granulētais superfosfāts (Ca(H2PO4)2 • H2O + CaSO4), un kālija mēslojums – kālija hlorīds (KCL). Granulu maisījuma veidošanai izmantoja šādas koksnes biomasas: bērzs (Betula pendula Roth.), kārkls (Salix spp.), baltalksnis (Alnus incana (L.) Moench.), apse (Populus tremula L.), hibrīdapse (Populus tremuloides × Populus tremula). Tās sausas koksnes pulveru veidā ieguva Latvijas Valsts mežzinātnes institūtā (LVMI) „Silava” Salaspilī. . Slāpekļa mēslojuma normu 30 kg haE-1 N un 180 kg haE-1 N ietekmē sausnas raža miežabrālim palielinājās no 17% līdz 53%, timotiņam – no 18% līdz 73%, pļavas auzenei – no 19% līdz 80%, niedru auzenei – no 10% līdz 59%, auzeņairenei – no 22% līdz 81%, un kamolzālei – no 30% līdz 73%. No stiebrzālēm saražotais enerģijas daudzums variēja no 93.6 GJ haE-1 (pļavas auzenei) līdz 112.1 GJ haE-1 (timotiņam). Veidojot koksnes maisījumus ar stiebrzāļu sugām, vairāk enerģijas tika iegūts no niedru auzenes un timotiņa proporcijā 3/1 (75% koksne + 25% stiebrzāles) – 141.9–146.4 GJ haE-1. Tika konstatēta likumsakarība: jo augstāks siltumspējas rādītājs, jo lētāka enerģijas pašizmaksa. Lētāko enerģiju, 3.68 EUR GJE-1, ieguva no timotiņa (augstākā siltumspēja – 16.88 MJ kgE-1), bet niedru auzenei un pļavas auzenei (augstākā siltumspēja – attiecīgi 15.24 un 15.71 MJ kgE-1) enerģijas pašizmaksa salīdzinājumā ar timotiņu palielinājās attiecīgi par 13% un 19%.