**6. Conclusion**

222 Biodiesel – Feedstocks and Processing Technologies

following considerations. Ammonium nitrate solution is prepared in an exothermic reaction of a ~65 % of nitric acid with ammonia gas, when an aqueous solution of NH4NO3 solution (roughly 80% ) is formed. Evaporation of this solution at high temperature leads to the melt of ammonium nitrate which is prilled in the next step of manufacturing. Since we use the NH4NO3 solution, which is contacted with the granules, the water removal, without melting of the NH4NO3, requires less energy than the final step of the solid NH4NO3 manufacturing. This concentrated NH4NO3 solution has acidic character, and easily react with the syngenite and other components of the eco-fertilizer. The concentrated NH4NO3 solutions are not only physically absorbed and imbibed in the pores of the eco-fertilizer, but chemically reacts with

K2Ca(SO4)2.H2O (syngenite) (NH4)2Ca(SO4)2.H2O(koktait) The potassium ions can be substituted with ammonium ion with the formation of partially or completely ion-exchanged syngenite-like isomorphous compounds. The completely substituted product is called to be koktaite, (NH4)2Ca(SO4)2.H2O, which is less soluble in water, thus releases nitrogen slowly into the soil (Angyal et al., 2006; Coates and Woodward, 1988; Von Maessenhausen et al., 1988). The formed potassium nitrate transformed into a solid solution with the excess of the ammonium nitrate, the typical composition of this product was the K0.27(NH4)0.73NO3. The koktaite and NH4-syngenites are sparingly soluble in water, thus the ammonium ion concentration liberated in the presence of water is constant at a given temperature and ionic strength of sulfate ion. Since not the full amount of the ammonium ion is liberated, no damages to the plant and losses by washing away, respectively occur even if using in high doses. When the plant absorbs the ammonium-ion from the soil, due to the equilibrium conditions, a part of the solid will dissolve and supply the water with a new amount of ammonium ion. Since the equilibrium concentration is closely constant, the amount of water will control the amount of the released ammonium ion, namely, the release of the ammonium ion from this koktaite type compounds is controlled by raining or irrigating. In drought situation, when there is no absorption of ammonium ion from the soil by the plant, there is no dissolution of ammonium syngenites and releasing ammonium ion which would be decomposed by the soil bacteria as it happens in case of water soluble ammonium ion containing fertilizers. Besides ammonium nitrate, other fertilizer components can also be used to adjust the main element concentrations, such as K, P or N, and to change the available form of these elements in various chemical compounds. The K2HPO4 does not react at all with other components of the ash. It is interesting, that ammonium salts as NH4Cl and (NH4)2SO4 cannot transform the syngenite completely into (NH4)2SO4, even if the ammonium sulfate is in excess, but in the presence of urea, the transformation is complete. Both KCl and K2SO4 decompose the ammonium syngenite, but the mixture of the K2SO4 and the NH4Cl produces (NH4)2Ca(SO4)2.H2O. Thus, the main factor is probably the ammonium to potassium ion ratio. There is an important difference between the behavior of the potassium sulfate and potassium chloride. The latter compound is more reactive, and KCl, KNO3 and NH4MgCl3 are also formed in its presence. Using various additives not only the ratio of the agriculturally important elements (K, P, N, S) are controlled but their chemical forms can also be altered. Using various kind of soil bacteria and supplementary materials to ensure theirs intensive growing is another possibility for nitrogen-fixation in the treated area. By using the eco-fertilizer technology supplemented

its components, as well.

By proper selection of biomass available from a given area, the sugar and energy sources, and the relative amount of the vegetable oil produced can be adjusted. In order to decrease the processing cost of raw materials into sugar containing mash for fermentation plants, the classical sugar sources as corn can be replaced with sugar sorghum, which can be processed similar to sugarcane. Combustion of the residual biomass in power plants or their digestion into biogas depend on the water and protein content of the residue and the heat or electricity demand of fuel-producing (biodiesel, biobutanol, acetals, etc.) or waste processing (fertilizer production) plants. Generally, it is more advantageous to use biomasses of high protein and water content in biogas plants. Burning the biogas or by using it as fuel in gas-engines the amount of heat and electricity can be controlled. Wastes of high cellulose content can be advantageously burned in power plants, sometimes after drying with the low heat value warm water streams of energy production. Wastes of fuel production can be utilized by combination these two methods of energy production. The ash and the solid residues from biomass power plants can be utilized as fertilizers by mixing them with potassium sulfate or calcium sulfate formed during recovery of the catalyst (KHSO4 or H2SO4) in biodiesel or acetal plants. Finally, there are two other wastes. The first is K2SO4 from the biodiesel technology, and the other is the ash from the combustion. Beyond the integration of energy producing and consuming plants and controlling the ratio of the raw materials and the type of the energy (heat or electricity), the production technology is also to be changed mainly in biodiesel, biobutanol and fertilizer plants. In this way the energy consumption of each technological step can be decreased.
