In Japan, the importance of utilizing biomass has been acknowledged as a part of the measures for the prevention of global warming. The "Biomass Nippon Strategy" was officially adopted as the basis for re-examining and furthering preventive measures. There are a number of means to turn biomass into energy : direct combustion, gasification, pyrolysis, anaerobic (methane) fermentation and hydrolysis, but "burning to use the heat" has been practiced ever since the dawn of history.
Burning biomass is considered a technology that grew and matured along with the development of the human society. Recently, high-pressure, high-temperature boilers are in demand to achieve high-efficiency power generation. To realize this, it is necessary to develop technologies in such areas as understanding and preventing the erosion caused by chlorine, understanding the behavior of low melting point ash and the prevention of clinker formation, and low-emission combustion.
Takuma has a long history of building and installing boilers. We have been building thermal recovery and power generation plants firing various biomasses since 1950's, and have acquired vast knowledge base and technologies concerning the nature and combustion of numerous biomass sources. In this article, we look into the history of the development of biomass combustion, together with the description of the characteristics of various biomass-burning technologies.
Boilers play an important role in every branch of the industry, and strong demands for improved energy efficiency and reduced environmental burden continue to be made upon them. In order to meet such demands, we have developed an innovative boiler with a drastically improved combustion performance.
The new boiler has a long, narrow combustion chamber that enables exhaust gas re-circulation, and is equipped with a special high-speed burner that forms thin-film flame.This combination has shown to achieve low NOx and CO emissions at a low air ratio.
The preceding article reports on the test result of the new concept boiler that is verified on the small boiler of the equivalent evaporation of 2,000kg / h and the total heat-transfer area below 10m2, firing city gas 13A.
We have developed a hot gas filter that collects dust from the exhaust gas at 700～900℃ from MSW incineration facilities in cooperation with Kyocera Corporation.
The filter element of the hot gas filter is made of sintered cordierite that has a heat-resistant up to 1,200℃. It has a dual layer structure with the filtration layer on the outer surface of the supporting tube. It has been confirmed that this filter element has high dust-capturing capacity, low filtration resistance, with excellent anti-corrosion quality against the exhaust gas from MSW incineration.
The filtration unit has a housing with boiler tube, and the elements are placed horizontally, supported at both ends. This arrangement enables stacking of the elements while retaining small footprint.
A pilot plant was built in order to confirm its performance. Exhaust gas from firing RDF was used for the test. The gas temperature was between 800～900℃ and the dust concentration was 5g / m3N at the filter inlet. The dust concentration at the filter outlet after chilling was 0.01～0.09g /m3N. Considering the evaporation of dust components, we consider the results satisfactory. The differential pressure through filters was 3.6kPa (at the filtration speed of 2m / min.), and the dioxins concentration of the captured dust was below 0.001 ng-TEQ /g.
We have continuously measured HCl concentration in the exhaust gas before particulate removal facility in four MSW incineration plants for a cumulative period of 293 days. From the results, it has been confirmed that the HCl concentration varies according to each plant, and the variation swings are relatively large within short periods of time. Spikes in excess of 1,000 ppm were observed, but these lasted just about 3 minutes, and the measured results remained below the designed values for almost all the period.
The total of the energy input into the plasma melting furnace is the product of the electric current and the voltage. With the same amount of energy input, operating conditions of a furnace can be changed by varying the current and the voltage. Because of the difference in size between the demonstration plant and the commercial plant, the optimum voltage for each may not be the same. We determined optimum voltage and current according to ash feed rate for the commercial plant based on the data from the demonstration plant by taking into consideration the furnace temperature of the commercial plant.
We decided to promote optimum operation by operating the commercial plant varying the voltage and the current, and comparing its operational characteristics. Test results showed that to run the furnace with higher voltage under stable plasma arc created even temperature distribution in the furnace, contributing to a continuous stable operation. It also reduced the electrode consumption by 30%.
The demonstration plant of alkaline pretreatment-hydrogen-methane fermentation of shochu distillation lees has been built in corporation with NEDO as an energy-recycling system in which the distillation lees generated in the production process of shochu is used to produce biogas that contains hydrogen and methane. The biogas is fired in a steam boiler and generates steam that is supplied back to the shochu distillery.
At the start-up of the methane fermentation, digested sewage sludge and wastewater sludge were used as the seed sludge, and the shochu distillation lees were fed when methane gas production was observed. The amounts of biogas production at start-up were approximately 38m3 / m3-sweet potato shochu distillation lees, and roughly 60m3 /m3-barley shochu distillation lees. These values matched those obtained from earlier laboratory tests.
Anammox (Anaerobic Ammonium Oxidation), a novel microbiological processes for removing nitrogen from wastewater, is attracting attention as it reduces the operational costs of aeration and carbon sources (e.g. methanol) compared with the conventional nitrification / denitrification system. Furthermore, it is expected to reduce its required equipment size thanks to the higher treatment speed. We applied this system for treating simulated wastewater and the effluent from methane fermentation of livestock (hog) manure, establishing the technology of nitrite production in the pretreatment process, and the anammox treatment system in its denitrification process. In the test using simulated wastewater, the maximum denitrification rate of 4.14kg / m3 / day has been achieved, while the treatment of effluent from methane fertilization that contained high-concentration nitrogen (NH4-N) has attained the maximum of 1.65kg / m3 / day. These results represent more than 80% nitrogen removal. From these tests, it has been established that anammox system applied to nitrogen removal from methane fermentation wastewater will reduce the plant size to less than one-half of the traditional systems.