An outline and recent trend is described about the structure and the mechanism related to the combustion of various gas cooking appliances. Cooking appliances are classified according to the kind of heating in cooking, and it introduces the feature of the equipment in a domestic and a commercial kitchen field. In a domestic kitchen field, thermal efficiency of gas cooking stove has improved by the newly developed burner. Thermal efficiency is increased to approx. 56% from approx. 46% with the conventional type. Since 2008, all gas cooking stoves have been required to be equipped with the safety sensors to comply with safety codes and standards in Japan. Installed functions are 'overheat prevention', 'auto-gas-shutoff function in emergency' and other functions by which enables automatic cooking. In a commercial kitchen field, there are special cooking equipments at each kind of cooking. In addition, various heats such as steam are used. The installation of the low radiative cooking equipment is recommended for a comfortable commercial kitchen.
Hot water plays an indispensable part of our present daily life. It can be conveniently usable for everyone since the instantaneous hot water heater was developed and widespread in the market. This term, convenience, actually means that we can use hot water with required temperature and quantity on demand. In the appliance, water flow and temperature sensors are actuated and calculate the amount of energy to create the hot water with requested temperature. To realize the supply of comfortable hot water in this process, combustion must be very significant phenomenon, which can convert the enthalpy of the fuel to the heat revelation quickly. Historically hot water heater has been changed to meet the needs of end users and observes regulations to protect the environment (downsizing, weight saving, low noise and low hazardous emission). According to the modification of hot water heater, burner has also been evolved so as to attain high-intensity combustion and high stability, namely from famous conventional Bunsen type burners to the present burner referred to as low NOx emission burner. It can achieve the lean combustion in which flame is surrounded with rich flame to compensate for its weak stability. These burners can be developed mainly by many engineers' aspiration with try-and-error activity rather than calculating with the fundamental academic knowledge of combustion. Presently, more distinguished burner improvement has been so hard because many configurations has been tried already, therefore, it is expected that new breakthrough invention will be created in the field of academic combustion study and will leads to the development of new fine burner.
Industrial once-through boilers regulated by “Boiler Safety Rules (in Japan)” were developed for increasing equivalent output (i.e. increasing heat release rate in furnace) against universal environmental standards have been more made more rigorous. Since this boiler type at the age 1960, boiler efficiency increases up to 96%, and also low emission technologies under high heat release rater were developed continuously against from low quality fuel as heavy oils spread at the Oil-Shocks to natural gas. At present, main fuels for boilers are shifted from regulated A-oil to natural gas (methane) due to environmental requirements and unstable global oil markets. Environmental standards qualities are more severely restricted about fixed emission facilities. Based on these environmental backgrounds, the progressive pre-mixed gas combustion techniques applied using flat surface burners against water tube bundle were developed and applied to low NOx emission as “Non-furnace combustion technique”. Approximately zero NOx emissions achieved with reducing catalysis and “Non-furnace combustion technique” at theoretical combustion air ratio that fuel gas flow controlled with sensing O2 concentration in combustion gas at exit. Based on this technique, the emissions of NOx and CO reduced within a few ppm at O2≒0~0.05% (nearly theoretical air ratio range).
Waste materials are classified into industrial wastes from industrial activities (4 billion t/y) and municipal wastes (50 million t/y). In 2003, electricity power generation from industrial waste was about 200,000 kW which was about one-sixth of that from municipal waste. However, since industrial wastes are composed of high calorie refuses, such as waste woods, sewage sludge, used oil, medical waste, they could be a prospective energy resource in the near future. Water-quenched step-wise mechanical stoker incinerators have been successfully utilized for high calorie refuses, while rotary kiln type is generally used for the incineration of used oil and medical wastes. Heat from incineration of wastes is recovered as hot water, hot air or steam. Steam boilers which are in practical use for municipal waste incineration do not meet economic requirement for incineration of industrial waste on a small scale (less than 100 t/d) because of fouling and erosion of heat exchanger. Recently, the author has revealed that there exists an optimum temperature range which gives effective heat recovery with heat exchanger though detailed observations and precise chemical analyses. The most promising methods of heat recovery from industrial wastes could be a heat container, which stores heat in an incineration site and transports it to heat utilization sites and a thermoelectric generator which converts temperature differences directly to electricity. Conversion efficiency of the thermoelectric generator is 4～5% at present, but it is a potential heat recovery method for small scale incinerators.
The demand of coal will increase in the world, especially in Asia by 2030. On the other hand, coal is a major source of CO2 emission. Development of clean coal technologies is necessary to meet the increasing demand and avoid rapid global warming. The major subject of coal utilization is reduction of CO2 emission from coal firing power plant and this paper reviews recent activities and developments of CO2 reduction technologies from coal firing power plant which are increase of the plant thermal efficiency by 700 degree advanced ultra supercritical boiler, use of biomass with coal and carbon capture and storage technologies. As increase of the demand, low rank coal (LRC) such as lignite and sub-bituminous coal, which has not been used as much as bituminous coal, is paid attention for future resources. Gasification technologies are suitable for LRC and a new type of gasifier is introduced.
Multiphase combustion is a complex phenomenon in which dispersion of liquid droplets or sold particles, their evaporation or devolatilization, and chemical reactions take place interactively at the same time, so that the underlying physics governing these processes has not been well understood and modeled especially for turbulent flows. With the remarkable progress in the performance of computers, the studies by means of direct numerical simulation (DNS) and large-eddy simulation (LES) of such turbulent multiphase combustion fields have recently been done. The DNS shows the detailed combustion behavior such that both premixed and diffusion flames coexist and droplet group combustion appears in spray flames. On the other hand, the LES is able to capture the general behavior of the spray and pulverized coal combustion fields in industrial equipments, although there still remain challenges towards the reliable prediction in terms of the mathematical models on turbulent combustion and pollutant emissions.
In this study, numerical simulation of high temperature combustion in CO-H2 mixture with oxygen jet has been conducted to consider post combustion in a converter for steel making process. In the numerical model, a coaxial flow diffusion flame was simulated, and the flammability characteristics and flame structure were examined. The influence of H2 content in the mixture and the reaction mechanism of the combustion were discussed. When H2 content in the mixture is high, the position of the highest temperature moves more upstream, and consumption of the oxygen is promoted. The total heat release rate in the combustion region becomes the maximum when H2 content in the mixture is 2% in volume. When the molar hydrogen concentration is over 20% in CO-H2 mixture, CO2 is decomposed around the edge of combustion zone, where the endothermic reaction occurs. Resultantly, the temperature in the downstream region is reduced. In the CO-H2 combustion, water vapor is also decomposed by the shift reaction of CO + H2O → CO2 + H2.
The effects of the unburned-gas temperature on the intrinsic instability of high-temperature premixed flames under the constant-enthalpy conditions were studied by two-dimensional unsteady calculations of reactive flows. A sinusoidal disturbance with sufficiently small amplitude was superimposed on a planar flame to obtain the relation between the growth rate and wave number, i.e. the dispersion relation. The growth rate increased as the unburned-gas temperature became higher, which was due to the increase in burning velocity of a planar flame. The linearly most unstable wave number, i.e. the critical wave number, was almost constant, indicating that the cell size was independent of the unburned-gas temperature. To elucidate the characteristics of cellular flames induced by intrinsic instability, a sinusoidal disturbance with the critical wave number was superimposed. The superimposed disturbance evolved, and a cellular-shaped front formed. As the unburned-gas temperature became higher, the behavior of cellular flames became milder, even though the growth rate increased. This was because that the difference in temperature between burned and unburned gases decreased owing to the constant-enthalpy conditions.