Wood pellets are a form of solid biomass energy and a renewable energy source. In 2015, the new and renewable energy (NRE) portion of wood pellets was 4.6% of the total primary energy in Korea. Wood pellets account for 6.2% of renewable energy consumption in Korea, the equivalent of 824,000 TOE (ton of oil equivalent, 10 million kcal). The burning phases of a wood pellet can be classified into three modes: (1) gasification; (2) flame burning and (3) charcoal burning. At each wood pellet burning mode, the volume and weight of the burning wood pellet can drastically change; these parameters are important to understand the wood pellet burning mechanism. We developed a new method for measuring the volume of a burning wood pellet that involves no contact. To measure the volume of a wood pellet, we take pictures of the wood pellet in each burning mode. The volume of a burning wood pellet can then be calculated by image processing. The difference between the calculation method using image processing and the direct measurement of a burning wood pellet in gasification mode is less than 8.8%. In gasification mode in this research, mass reduction of the wood pellet is 37% and volume reduction of the wood pellet is 7%. Whereas in charcoal burning mode, mass reduction of the wood pellet is 10% and volume reduction of the wood pellet is 41%. By measuring volume using image processing, continuous and non-interruptive volume measurements for various solid fuels are possible and can provide more detailed information for CFD (computational fluid dynamics) analysis.

Extended Abstract In recent years, domestic and overseas industrial boilers have achieved high thermal efficiencies up to 90%. Industrial boiler manufacturers and research institutes are working to increase the thermal efficiency and reduce carbon monoxide (CO) and nitrogen oxide (NOx) in a flue gas of boiler. Korea has been supporting subsidies for a low NOx burner when nitrogen oxides in flue gas are lower than 40 ppm (4% O2) for LNG burner, and NOx concentration for lowest certified burner at 2016 in Korea was 8.8 ppm. But the burner characteristics are changed due to a variation of surrounding environment, burner aging due to an operation and so on. Therefore NOx and O2 concentrations can be changed with an operation time of burner. By using Smart NOx Sensor (Continental AG) which can measure NOx and O2, the possibility of using the sensor for measuring the oxygen concentration and the NOx value simultaneously in a flue gas was confirmed in industrial boiler. The sensor precision was confirmed in a NOx and O2 standard gas before boiler installation. Results said that O2 and NOx output value of the sensor are 0.45 % and 49 ppm in a case of O2 0 % and NOx 48.8 ppm standard gas. With the Smart NOx sensor, flue gas concentrations in an industrial boiler were measured and compared by conventional flue gas analyzer (Testo 350). The smart NOx sensor has faster responsibility than the flue gas analyzer due to an insert type characteristic. With the sensor, real-time control O2 and NOx of flue gas can be obtained by using flue gas recirculation, combustion air fan control system and burner geometry control. This work was conducted under framework of the research and development program of Korea Institute of Energy Technology Evaluation and Planning (No. 20152020105290) and Korea Institute for Advancement of Technology (NO. 10070223).

Spent Coffee Grotind is a residue of coffee drink mainly used at a coffee shop. Spent coffee ground is used as an odor removal, manure in flowerpot and so on. However most of spent coffee ground is discarded as garbage. In this study, we investigated characteristics of spent coffee ground as a fuel and combustion characteristics in a small boiler system (6.5 kW based on input lower heating value), such as CO, NOR, O-2 and heating characteristic of heating boiler. Drying of spent coffee ground in the open air condition takes less than 6 days in case of height of 11 mm. More than 96% of spend coffee ground is between 100 and 500 gm in particle size. Lower heating value of spent coffee ground used as fuel is about 18.8 MJ/kg (4500 kcal/kg at water content 10%). Combustion chamber of the boiler is a crucible type with primary and secondary air supply and heat exchanger is one through type. Spent coffee ground consumption as a fuel of the boiler is about 1.17 kg/hr. O-2 concentration of the flue gas of the boiler is about 17.8% which is higher than a commercial domestic gas boiler or a domestic wood pellet boiler. CO and NOx concentration are 643 and 163 ppm respectively. (C) 2017 Elsevier Ltd. All rights reserved.

A grate-firing boiler was developed for wood pellet fuel, and then its combustion characteristics were tested. The flame was stretched to the exit of the combustion chamber, implying insufficient space for complete combustion. As a first step to resolve this problem, a numerical simulation was conducted for the combustion chamber. Turbulent and chemically reacting flow was considered by implementing a homogeneous reaction model. Flow field from the simulation showed strong recirculation flow at the upstream corner of the chamber, along which the flame was stretched to the exit. Based on these results, we suggest possible modification of the combustion chamber to improve combustion characteristics, such as relocating its exit or installing internals like guide vanes.

Wood pellets are a kind of solid biomass energy and a renewable energy source. Made by compressing sawdust, wood pellets have a higher energy density than split firewood and wood chips. In 2007, the new and renewable energy (NRE) portion was 2.4% with respect to total primary energy in Korea. The Korean government wants to increase the new and renewable energy (NRE) portion up to 6.1% by 2020 [1]. To achieve this target, the government has been establishing some policies, such as incentive policy, NRE mandatory use for public building and renewable portfolio standard (RPS) and so on. To supply wood pellets as fuel for the combustion chamber of a wood pellet boiler, most domestic wood pellet boilers put a constant volume by using an auger type fuel feed system. In an auger system as fuel feeding, there is the possibility of changing energy input due to the different density of wood pellets even in a constant volume flow rate of wood pellets. If fuel input rate is changed without any correction of air flow rate for combustion, the condition of combustion in a wood pellet boiler can be deteriorated. We have developed an air-fuel control system for a domestic wood pellet boiler by using flue gas oxygen concentration measurement and a PID controller. To measure O2 concentration of flue gas, a wide band O2 sensor was adopted. We changed fuel input from 100% to 50% by artificial manipulation to confirm the control system. The O2 concentration in flue gas can be controlled to be 8.5% ± 1% without significant change of CO and NOx concentration.

Wood pellet is solid biomass energy and one of renewable energy sources. In 2008, new and renewable energy (NRE) portion is 2.4% with respect to total primary energy in Korea. Korea government wants to increase new and renewable energy portion up to 6.1% by 2020 [1]. To achieve the target of NRE portion, Korea government has been establishing some policies, such as incentive policy, NRE mandatory use for public building and renewable portfolio standard (RPS) and so on. One of these policies is a domestic wood pellet boiler supply policy. But wood pellet boiler manufacturers who want to participate in the supply policy need a performance test result from a qualified test institute such as Korea Institute of Energy Research (KIER) and Korea Testing Laboratory (KTL). So we install a test facility to evaluate heating performance of a domestic wood pellet boiler semi-automatically.In order to achieve a thermal efficiency of a wood pellet boiler, it is very important to maintain heating water inlet and outlet temperature and water flow rate to be stable. We use 2 water passages in the system; one is circulation of a wood pellet boiler heating water passage and the other is a cooling circulation for removal heat from the wood pellet boiler. These 2 water passages exchange heat by a plate type heat exchanger. We control the flow rate of cooling water based on the wood pellet boiler water inlet temperature. With this system, temperature variation of boiler inlet and outlet temperature is less than 0.4 degrees C, that is +/- 0.2 degrees C which is important to evaluate boiler thermal efficiency. (C) 2012 Elsevier Ltd. All rights reserved.

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.

A finned-tube-type evaporator module has been proposed for a 2 t/h-class water-tube-type industrial boiler with multiple burners. The geometry of the fins was changed at each module to equalize the evaporation. The modules were designed by considering the energy balance at each row rather than by following a conventional bulk design procedure. The designed module was built into a 2 t/h-class water-tube-type boiler, and its performance was tested. A numerical simulation was also conducted to evaluate the two- or three-dimensional effects of factors such as the inlet conditions. The numerical simulation also included the conjugate heat transfer problem to predict the fin tip temperature. The heat transfer coefficient with fins is lower than that obtained from the empirical correlation of a bare tube. The fin tip temperature from CFD is higher than that from the analytical solution.

A 0.5 t/h class non-furnace boiler has been developed with the aim of achieving a high efficiency and compactness. A metal fiber burner has been adopted so that a stable flame can be obtained. The tube banks are installed downstream of the burner. Bare tubes are used upstream, while finned tubes are installed downstream. The heat-transfer characteristics of the non-furnace boiler have been studies on the basis of the results of the numerical simulation as well as those of the experiment. Important design parameters such as the bulk temperature along the streamwise direction and the temperature of the fin tips have been evaluated using the CFD results and compared with the experimental data and the empirical correlations typically used for the design of the boiler.

We conducted a test of a direct burning of crude Jatropha oil (CJO) and pitch in a commercial boiler system. The fuel, crude Jatropha oil is not biodiesel which comes from transesterification process of bio oil, but it is pure plant oil like cooking oil. The higher heating value (HHV) of the CJO is 39.3 MJ/kg (9380 kcal/kg) and is lower than that of commercial heating oil, 44.0 MJ/kg. The kinematic viscosity of CJO is 36.2 mm2/s at 40 °C and 8.0 mm2/s at 100 °C. The burner used in the test is a commercial burner for a commercial heating oil and its capacity is 140 kW (120,000 kcal/h). We did a preliminary test whether the combustion is stable or not. The preliminary test was a kind of open air combustion test using the commercial burner with crude Jatropha oil. We found that the combustion can be stable if the crude Jatropha oil temperature is higher than 90 °C. We measured the flue gas concentration by using a gas analyzer. The NOx concentration of crude Jatropha oil is 80 ∼ 100 ppm and CO concentration is nearly 0 ppm at flue gas O2 concentration of 2.5 and 4.5%. We also tested a pitch combustion and the result shows that the NOx concentration of pitch is about 90 ∼ 110 ppm and CO concentration is below 30 ppm at flue gas O2 concentration of 2.5 and 4.5%. As a reference data, combustion of heating oil was conducted. The NOx concentration of heating oil is about 80 ppm which is the lowest value of tested fuels.

Recently domestic wood pellet boilers are installed in rural and forestry houses. The fuel price per lower heating value of wood pellet is about 20 % lower than that of heating oil on July 2010. In spite of lower price of wood pellet, a few user of wood pellet boiler complain expensive fuel cost. One of this reason is inaccurate or improper air-fuel ratio setting of wood pellet boiler. O2 concentration of flue gas of domestic wood pellet boiler is about 9.7 % and there are few domestic wood pellet boiler which can control air-fuel ratio automatically. We tested a domestic wood pellet boiler in changing boiler thermal output and air-fuel ratio. The nominal boiler thermal output is 25 kW (21 500 kcal/h). We measured thermal efficiency and flue gas concentrations such as CO and NOx at each boiler thermal load with various air-fuel ratio. The results show that if air flow rate is the same as full load and part load, thermal efficiency of part load of 40 % drops about 7.7 %p compared to boiler full load case.

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.

We investigated combustion characteristics of wood pellets in a combustion equipment with adjusting amount of flue gas. Maximum temperature in a combustion chamber was $850^{\circ}C$ . Higher heating Value of a domestic wood pellet tested is 19.1 MJ/kg and water content was 8.3%. Amount of flue ga...