報告書番号

U39

タイトル（和文）

石炭の生物加工 －１６－ --微生物による石炭改質技術に関する総合報告--

タイトル（英文）

Bioprocessing of coal ‐16- - Coal cleaning by bacteria -

概要 （図表や脚注は「報告書全文」に掲載しております）

将来の低品位炭の活用を目的とし、微生物を利用したコールクリーニングについて検討した。微生物（鉄酸化細菌）を物理的選炭法である浮遊選炭に微生物界面活性剤として利用することで、石炭中の無機硫黄である黄鉄鉱を除去でき、脱硫と脱灰が同時に可能となった。細菌は脱硫と脱灰が同時に可能となった。細菌は自身が持つ特殊なタンパク質によって黄鉄鉱の還元状態の鉄を認識して選択的に吸着した。また、この細菌は鉄を介して電極から電気エネルギーを供給することで連続的に生産できた。この細菌の生産と浮遊選炭を組み合わせたベンチスケールシステムを試作・運転した結果、本システムにより６７％の黄鉄鉱硫黄と同時に３５％の灰分を除去できた。また、可燃分の回収率は８０％であった。低品位炭を燃焼前に改質することで、発電用炭の開拓に役立つと考えられた。

概要 （英文）

Coal is an important primary energy sources for power generation. However, there are some disadvantages in the usage of coal. As coal contains sulfur and ash, it is necessary to treat fuel gases for removal of sulfur dioxide and coal ash for reuse. Although low sulfur and ash coals are selected to combust for power generation at present, it will be required to use high sulfur and ash coals in future. In resent several years, it is focusing to reduce sulfur and ash contents of coal before combustion. Those coal cleaning technologies may be not only useful to extent coal mass for power generation but also to reduce treatment processes for fuel gas and ash. Here we report coal cleaning technology with bacteria for the use of high sulfur and ash coal. Coals contain pyrite as inorganic sulfur in carbon matrix. Flotation has been known as one of physical coal cleaning methods and can separate hydrophilic particles from a mixture of hydrophilic and hydrophobic particles on the basis of the differences in the surface properties between particles. However, it seems to be difficult to separate coal and pyrite particles by this method due to hydrophobicities of coal and pyrite particles. However, it is succeeded to enhance pyrite removal in the floatation by the addition of iron-oxidizing bacterium. The bacterial cells can adhere to the pyrite particles, and the adhesion change the surface property of pyrite from hydrophobic to hydrophilic by surrounding pyrite particles. In this manner, microbial flotation can remove pyrite from coal as well as ash because ash particles are hydrophilic. The detail of adhesion of iron-oxidizing bacterium to pyrite is clarified. The bacterium synthesizes the specific protein for the adhesion on the cell surfaces. The protein mediates the adhesion of the cells through the chemical bonding between the reduced iron in pyrite and three ligands on the protein molecules. Therefore, the bacterium is able to adhere selectively to pyrite. As a result of the selectivity, the bacterial cells behave as a biological surfactant for pyrite in flotation. The iron-oxidizing bacterium takes energy for growth from the oxidation of ferrous irons to ferric ions. It is possible to enhance yields of the cells by the reduction of ferric ions to ferrous ions using an electrode. The growth is enhanced by continuous supply of ferrous irons as an electron mediator. In continuous cultivation system, it is proved that the system produces the cells at the 4.3×109 per a day for 40 days. In batch operation, pyrite and ash removal is reached to 70% and 57%, respectively. Therefore, a semi-continuous system composing of culture tank and flotation is established to confirm pyrite and ash removal from high sulfur and ash coal. The system rejects 67% of pyrite and 35% of ash from the fed coal. At the same operation, the combustable recovery of the coal is 80%. Economical effect on 100kW of power generation plant is estimated in the case that coal cleaning is applied to coal production site at China. The economic trail is estimated separately for coal cleaning, transportation, fuel gas treatment and ash reuse in the case that high sulfur and ash coal is converted by coal cleaning for power generation. As a result of coal cleaning, the reduction of cost for transportation and ash reuse is much greater than that for fuel gas treatment. Although those effects is depending upon the sulfur and ash contents of coals, the total economic effect is estimated as approximately ten million yen.

報告者

キーワード