Joon Ahn

CFD (Computational Fluid Dynamics) Study on Partial-Load Combustion Characteristics of a 4-Step-Grate Wood Pellet Boiler

A numerical simulation was conducted for the combustion chamber of a 4-step grate-firing boiler for wood pellet fuel. The flame is extended to the exit of combustion chamber, which is reproduced by present numerical method based on a homogeneous reaction model. Flow field from the simulation shows a strong recirculation flow at the upstream corner of the chamber, along which the flame is extended to the exit. These combustion and flow characteristics remain unchanged for partial load operations, which suggest modification of the combustion chamber structure rather than resizing should be effective to improve combustion characteristics. Possible modifications for combustion chamber are suggested such as relocating its exit, increasing the number of grate steps or installing internals such as guide baffles.

Combustion Characteristics of a Staged Burner for a Boiler

The demand for a boiler with low NOx burner is increasing with the recent strict NOx regulation. Staged burner is a common low NOx burner to suppress the formation of thermal NOx by yielding local fuel rich and lean condition. The staged burner gives fire with bigger frontal area and length compared with a conventional burner, which changes heat transfer characteristics in the combustion chamber. The heat transfer and exhaust gas characteristics have been studied in the present study for a 0.5 t/h class furnace type boiler adopting the staged burner. A numerical simulation has been conducted to clarify the detailed physics inside the combustion chamber.

Impact of Residential CHP Systems on Greenhouse Gas Emissions in Korea

The effects of applying the micro CHP system to the domestic sector in Korea were investigated using annual cooling and heating demand data. Four prime movers, micro gas turbine, PEMFC, gas engine and Stirling engine, were compared for three operational modes. Two way buy-back was assumed for both electricity and heat. The Stirling engine gave the lowest emission per energy for 300kWh monthly electricity production. However, PEMFC became more effective when considering PURPA criteria. PEMFC generated the least greenhouse gas with higher electrical efficiency for cooling. The Stirling engine, however, became competitive for heating with higher total efficiency.

Performance of a Hybrid Desiccant Cooling System in a Residential Environment

A series of field tests of hybrid desiccant cooling systems was conducted during July and August 2012. The temperature and humidity of supply and return air and power and heat consumption were monitored, and data were transferred in real time through the internet. The performance of the cooling system (i.e., cooling capacity and the coefficient of performance [COP]) was evaluated from measured data and variations with regard to outdoor conditions were analyzed. The cooling capacity decreased with an increase of outdoor temperature, while it increased as outdoor humidity increased. The COP also increased with an increase in outdoor humidity. However, the dependence of the COP on outdoor temperature was rather weak.

Combustion Characteristics of a Premixed Burner in a Stirling Engine for a Domestic Cogeneration System

최근 에너지 자원의 고갈과 지구 온난화 문제가 심각하게 인식되면서 장기적으로는 신재생 에너지의 개발이 단기적으로는 에너지의 합리적 이용이 대책으로 제안되고 있다. 에너지의 합리적 이용 방안으로서 가용 에너지 및 엑서지의 개념에 바탕을 둔 계단식 열에너지 이용을 고려할 수 있다. 즉, 연료를 연소함으로써 발생한 고온의 열에너지는 1 차적으로 전기 에너지로 변환하고 냉난방을 위해 필요한 열은 변환 후에 발생하는 배열을 이용하면 가용에너지가 높은 연소 가스를 직접 열로서 활용하는 것보다 에너지를 합리적으로 활용할 수 있다. 위와 같은 에너지 이용방식을 열병합 발전이라고 하고 시스템을 소형화하여 에너지 수용가에서 직접 전기 및 열에너지를 생산하여 활용할 경우, 고압 송전을 위한 변압 과정이나 송배전 과정에서 발생하는 에너지 손실을 줄일 수 있을 뿐 아니라 에너지 수요에 맞추어 에너지를 생산함으로써 에 Key Words: Stirling Engine(스털링 엔진), Burner(버너), Premixed Combustion(예혼합 연소), Surface Combustion (표면 연소) 초록: 화석 에너지 고갈에 따라 에너지의 합리적 이용이 요구되면서 가용 에너지를 고려한 열에너지의 계단식 활용이 적극적으로 검토되고 있다. 이와 같은 배경에서 1 kW 급의 스털링 엔진을 기반으로 한 열병합발전 시스템이 분산 에너지 시스템을 구축하는 단위로서 제안되었다. 1 kW 의 용량은 가정용에 적합하며, 가정에서 활용하기 위해서는 공간을 작게 차지하도록 하면서도 소음과 유해가스의 배출을 철저하게 차단해야 한다. 이러한 조건들을 충족시키며 효율이 높은 시스템을 개발하기 위하여 슬롯 형태의 예혼합 버너를 제안하였고 버너의 연소 특성을 파악하기 위하여 일련의 실험을 수행하였다. 본 연구에서는 화염의 형상을 촬영하여 연소부하 및 공기비에 따른 연소 모드를 관찰하였고 배가스를 분석하여 연소 모드에 따른 배기 특성을 연구하였다. Abstract: The availability of thermal energy has been widely recognized recently, and the cascade usage of thermal energy from combustion has been encouraged. Within this framework, a 1-kW-class Stirling-engine–based cogeneration system has been proposed as a unit of a distributed energy system. The capacity has been designed to be adequate for domestic usage, which requires high compactness as well as low emissions and noise. To develop a highly efficient system satisfying these requirements, a premixed slot-type short-flame burner has been proposed, and a series of experiments has been performed to understand its combustion characteristics. Flame images have been captured to observe the dependence of the flame mode on the combustion load and air/fuel ratio. The exhaust gas has been sampled and analyzed to study the emission characteristics for each flame mode.

Combustion Characteristics of Non-premixed VIStA Burner in Once-Through-Type Boiler

A modified VIStA (vortex inertial staged air) burner was developed and used in a once-through-type boiler. For safety, the combustion in this burner is of the non-premixed type. An air damper is installed to control the distribution of air to each combustion chamber. The effects of the air-fuel ratio and air distribution on NOx formation were investigated. The newly modified VIStA burner gives NOx reduction effect by maximum 20% in the combustion chamber of a boiler, while it yields more uniform flame than the conventional burner.

Performance Analysis of Hybrid Desiccant Chiller Based on Field Test

Field tests of hybrid desiccant cooling systems were conducted from July to August 2011. Data were monitored and transferred in real time over the Internet. The monitored variableswere analyzed to determine the performance characteristics under outdoor conditions. A series of system simulations has been conducted for outdoor conditions of the field tests. The results agree well with the experimental data in general. The system performance has been shown to deteriorate for wetter conditions, as predicted by the simulation.

Performance Characteristics of a Regenerative Heat Exchanger Depending on Its Porous Structure

Stirling engine is an external combustion engine, whose efficiency approaches that of Carnot engine with the help of a regenerator. The regenerator is a heat exchanger composed of porous medium, whose performance is dependent on the pore structure. Three types of pore structures are considered in the present study. They are wire screen, random wire and composite structure, i.e. a combination of wire screens with different hydraulic diameters. The porosity more highly affects the performance of a regenerator compared to the hydraulic diameter. The random wire can yield high effectiveness even at a high porosity. The composite mesh gives better performance when the hydraulic diameter decreases in the direction from hot side to cold side.

COMBUSTION SIMULATION OF 1 kW CLASS LNG STIRLING ENGINE CHP SYSTEM CONSIDERING HEAT RECOVERY

As fossil fuel has been depleted, a reasonable use of energy is required. In this regard, the cascade use of thermal energy has been proactively considered in view of available energy. For the purpose, the micro co-generation system for a household based on Stirling engine was suggested as a unit of distributed energy system. A slot-type premixed burner is used to completely block noises and harmful gases for the purpose of use in a household, and air supplied to a burner recovers heat from the exhaust gas in order to improve the efficiency of energy use. This study conducted a numerical simulation on combustion in a combustion chamber to investigate the effects that recuperation of heat from exhaust gas have on heat transfer and combustion characteristics.

Heat Transfer Characteristics of Heat Exchange Module for a Water Tube Type Modular Boiler

A finned tube type heat exchange module has been proposed for a multi-burner water tube boiler. Fin density and length increase in streamwise direction to equalize the evaporation for each module, which makes it difficult to apply conventional bulk design procedure. The design program has been improved by updating data for every row of tubes along the flow. A numerical simulation has been also conducted to evaluate the effect of inlet conditions and validated with experiment. The heat transfer of the first row has been underpredicted by the conventional Zhukauskas correlation, since the acceleration of the flow due to the blockage is not fully inflected. The fin tip temperature is also underpredicted by Bessel solution, because of the interaction with neighboring fins.