Stainless Steel Combustor Research Articles

Numerical investigation on flame blow-off limit of a novel microscale Swiss-roll combustor with a bluff-body

A micro Swiss-roll combustor with a bluff-body was proposed for the first time. It is demonstrated that this improved design can greatly extend flame blow-off limit by reducing the flame stretch effect. The flame stabilization ability of this new combustor made of quartz, stainless steel (SS) and silicon carbide (SiC) was numerically investigated using a three dimensional, steady state, k-epsilon turbulence model. The results show that at an equivalence ratio of 0.5, the blow-off limits of quartz combustor, SS combustor and SiC combustor are 40 m/s, 50 m/s and 35 m/s, respectively. Comprehensive analyses were conducted under an inlet velocity of 20 m/s. It was revealled that the heat loss rates for quartz, SS and SiC combustors were 153 W, 108 W and 185 W, respectively. The SS combustor has the best heat-recirculation effect, followed by quartz combustor and SiC combustor. The lengths of recirculation zones are 4.35 mm, 3.4 mm and 3.37 mm for SiC combustor, quartz combustor and SS combustor, respectively. In summary, the heat loss rate is the chief factor responsible for the flame blow-off limit of this novel Swiss-roll combustor. It acts together with the heat-recirculation effect and flow-recirculation effect to determine the flame blow-off limit.

Preliminary design of an optically accessible high-pressure combustor

Future generation gas turbine combustors for power production are expected to have the capability of operating on a variety of different types of fuels. Energy systems running on different fuels produce flames with different burning behaviors, combustion dynamics, and pollutant emissions than when using conventional fuels. To ensure the implementation of new energy sources for future power generation units, which is critical for the US energy sector, lab-scale studies at high pressures and temperatures are being performed at many different locations throughout the world. Although many of these authors in the past present their results from the use of a high-pressure combustor, none have made their design methodology available to the public. Therefore, this paper presents a design of an optically accessible high-pressure combustor facility based on a 500 kW power and 1.5 MPa capability, which is the representative pressure of a gas turbine. Finite element analysis was extensively used to predict window and wall thicknesses needed to withstand these extreme conditions. Based on stress analysis quartz windows were designed with a thickness of 48 mm and a thickness of 8.61 cm was selected for the stainless steel combustor. Follow-up on testing using the high-pressure gas turbine combustor using various different types of fuels, diluents, and injectors have provided repeatable data on the capability of the combustor design to withstand the extreme environment conditions.

Emissions of SO3 from a Coal-Fired Fluidized Bed under Normal and Staged Combustion

This paper reports the measurements of SO3 emissions with and without limestone under unstaged and staged fluidized-bed combustion, carried out on a m2 and 2 m high stainless-steel combustor at atmospheric pressure. The secondary air was injected 100 cm above the distributor. SO3 emissions were monitored for staging levels of 85 : 15, 70 : 30, and 60 : 40, equivalent to a primary air/coal ratio (PACR) of ~0.86, 0.75, and 0.67. Experiments were carried out at 0%–60% excess air level, 1-2 m/s fluidizing velocity, 800–850°C bed temperature, and 20–30 cm bed height. During unstaged combustion runs, SO3 emissions were monitored for a wide range of Ca/S ratios from 0.5 to 13. However, for the staged combustion runs, the Ca/S ratio was fixed at 3. SO3 was retained to a lesser extent than SO2, suggesting that SO2 reacts preferentially with CaO and that SO3 is involved in the sulphation process to a lesser degree. The SO3 emissions were found to be affected by excess air, whereas the fluidizing velocity and bed temperature had little effect. SO3 was depressed on the addition of limestone during both the staged and unstaged operations, and the extent of the reduction was higher under staged combustion.

Catalytic Effect of Microcombustion in Microthermophotovoltaic System

In this work, we present experimental results in a platinum microcombustor. The experimental results show that owing to the catalytic effect of platinum, both the temperatures along the wall and on the exit plane of the platinum microcombustor are much higher than that of the stainless steel combustor under the same testing conditions. The increase of temperature near the wall is more obvious than that near the center region. The results suggest that the catalytic reaction overwhelms the gas-phase combustion. The higher surface area to volume ratio in a microcombustor makes area-limited catalytic combustion even more attractive. Strong effect of flow rate (Re number) on catalytic combustion is also identified. The experiment was further extended to a prototype micro-TPV system. At a mass flow rate of hydrogen 4.2 × 10−3 kg/h and H2/air ratio of 0.9, the system is able to deliver electrical power output 0.785 W. The measured open-circuit voltage and short-circuit current are 2.32 V and 0.445 amps, respectively.

Zero test emissions of sulphur dioxide from large coal under staged fluidized bed combustion

This paper reports the emissions of SO2 from large coal under staged combustion without any additive. A stainless steel combustor, 2 m high and 0.3 × 0.3 m in cross section was used. Fluidizing air was supplied through a multihole distributor. An adjustable secondary air injector was used along the vertical axis of the combustor to introduce secondary air in the freeboard. From 0–40% of total air was injected in the freeboard above the bed. The experiments were carried out at fluidizing velocities of 1–2 m s-1, bed temperatures of 1103–1153 °K, 20–40% excess air, and bed particle sizes of 665 μm. Bed temperature and level of air staging had the most significant effect on SO2 emissions.

Reduction of SO 2 emissions from a fluidized bed under staged combustion by fine limestone

This paper considers the effects of operating variables on SO 2 emission in staged combustion with a stainless steel combustor 2 m high with a 0.3 × 0.3 m cross section. Fluidizing air was supplied through a multihole distributor. The experiments were carried out for fluidizing velocities of 1–2 m/s, bed temperature of 830–880°C, 20–40% excess air, and bed particle sizes of 0.313 and 0.655 mm. The bed temperature, fluidizing velocity, and excess air level had a significant effect on SO 2 emissions reduction during staged combustion. A maximum reduction of 64% was obtained at 70:30 stage, 830°C bed temperature and 1.0 m/s fluidizing velocity. The zero or negative emissions reduction resulted from the balance between the SO 2 pick-up by limestone in the region where oxidizing conditions prevail (due to a higher stage level, i.e. 60:40) and the release of SO 2, already captured elsewhere in the combustor, from CaSO 4 in reducing regions (due to higher stage and low excess air).

96/02195 Total equivalent warming impact of refrigerants

To meet the legislation on limiting NOx and SOx emission from large combustion plants, SO2 emissions may need to be reduced by about 60–70%. The authors' technique for achieving significant reduction in SO2 emissions from combustion systems burning large coals utilizes limestone for in situ reduction of SO2 in fluidized bed combustors. A recent technique for reducing NOx emissions combines staged combustion with ammonia injection. However, concern has arisen about the effect of low primary air:coal ratio (PACR), and hence low bed oxygen levels, on the rate of reaction between calcined limestone and SO2. This paper reports on the significance of air-staging on the reduction of SO2 emissions by limestone in a fluidized bed combustor. The experimental rig consisted of a stainless steel combustor 2 m high and 0.3 m2 in section. Fluidizing air was supplied through a multihole distributor and secondary air was introduced into the freeboard via an injector whose height could be adjusted. The experiments were carried out at overall fluidizing velocities between 1 and 2 m s−1, bed temperatures of 830–880°C, 5–40% excess air levels and bed particle size of 313 + 690 μm. Various levels of air-staging (10–50%) were investigated (equivalent to PACRs of between 0.84 and 1.4, respectively). An uncooled sampling probe located at the cyclone exit was used to determine SO2. The results showed that SO2 emissions could be reduced by over 50% using limestone under unstaged combustion conditions. There was little effect of staged combustion on SOx emissions without limestone. When limestone was used, the effectiveness of sulfur capture decreased (by almost 50%) as the level of air-staging was increased. The bed temperature had the most significant effect on sulfur retention by limestone (10% at 880°C to almost 60% at 830°C). A decrease in overall fluidizing velocity resulted in an increase in SOx reduction. The present work has provided significant data on the parameters that influence SOx retention by limestone during staged combustion.

SO X emissions from a fluidized-bed combustor with and without limestone addition

We consider the effects of operating variables on SO X emissions in unstaged combustion with a stainless steel combustor that is 2 m high and has a 0.3 m × 0.3 m square cross section. Fluidizing air was supplied through a multihole distributor. The experiments were carried out for fluidizing velocities of 1–2 m/sec, bed temperatures of 830–880°C, 20–40% excess air, and bed particle sizes of 665 μm. SO X emissions were reduced by over 70% with limestone. The bed temperature had the most significant effect on sulphur retention. Decreases in fluidizing velocity and increases in excess air result in increased SO X reduction.

The effect of limestone particle size on sulphur dioxide retention in a fluidized bed combustor

This paper reports on the effect of limestone particle size and operating parameters on the reduction of sulphur dioxide emissions in a fluidized bed combustor operating under unstaged combustion conditions. The experimental rig consisted of a stainless steel combustor, 2 m high and 0.3 m square in section. The experiments were carried out at overall fluidizing velocities between 1–2 m/s, bed temperature 830–880°C, 20–40% excess air level, bed particle size of 665 μm and limestone particle size between 0.8–3 mm mean diameter. An uncooled sampling probe located at the cyclone exit was used to determine sulphur dioxide. The results showed that the bed temperature had the most significant effect on sulphur dioxide retention. An increase in excess air level and decrease in limestone particle size resulted in an increase in sulphur dioxide reduction. Over 70% reduction could be achieved using coarse (1–2 mm) limestone under unstaged combustion conditions.

The influence of air staging in the reduction of SO 2 by limestone in a fluidized bed combustor

To meet the legislation on limiting NO x and SO x emission from large combustion plants, SO 2 emissions may need to be reduced by about 60–70%. The authors' technique for achieving significant reduction in SO 2 emissions from combustion systems burning large coals utilizes limestone for in situ reduction of SO 2 in fluidized bed combustors. A recent technique for reducing NO x emissions combines staged combustion with ammonia injection. However, concern has arisen about the effect of low primary air:coal ratio (PACR), and hence low bed oxygen levels, on the rate of reaction between calcined limestone and SO 2. This paper reports on the significance of air-staging on the reduction of SO 2 emissions by limestone in a fluidized bed combustor. The experimental rig consisted of a stainless steel combustor 2 m high and 0.3 m 2 in section. Fluidizing air was supplied through a multihole distributor and secondary air was introduced into the freeboard via an injector whose height could be adjusted. The experiments were carried out at overall fluidizing velocities between 1 and 2 m s −1, bed temperatures of 830–880°C, 5–40% excess air levels and bed particle size of 313 + 690 μm. Various levels of air-staging (10–50%) were investigated (equivalent to PACRs of between 0.84 and 1.4, respectively). An uncooled sampling probe located at the cyclone exit was used to determine SO 2. The results showed that SO 2 emissions could be reduced by over 50% using limestone under unstaged combustion conditions. There was little effect of staged combustion on SO x emissions without limestone. When limestone was used, the effectiveness of sulfur capture decreased (by almost 50%) as the level of air-staging was increased. The bed temperature had the most significant effect on sulfur retention by limestone (10% at 880°C to almost 60% at 830°C). A decrease in overall fluidizing velocity resulted in an increase in SO x reduction. The present work has provided significant data on the parameters that influence SO x retention by limestone during staged combustion.

The reduction of NOx emissions from a fluidized bed combustor by staged combustion combined with ammonia addition

The European Economic Community is proposing legislation aimed at limiting NO x , SO x and particulate emissions from large combustion plants. The limit values proposed indicate that NO x emissions from the present generation of atmospheric fluidized bed combustors, burning large coals (6–25 mm) in shallow beds, may need to be reduced by up to 50%. This paper reports on an investigation in which air-staging is combined with gaseous ammonia injection, for the reduction of NO x emissions. The experimental rig consisted of a stainless steel combustor, 2 m high and 0.3 m square in section. Fluidzing air was supplied through a tuyure distributor and secondary air was introduced into the freeboard via an injector whose height could be adjusted. Ammonia was injected over the bed surface. The experiments were carried out at an overall fluidizing velocity of 2 m/s, bed temperature 870 C and 40% excess air. Combustion gases were sampled by probes located at various locations in the combustor and also by a vertical probe that could scan the total length of the combustor. A 50% reduction in NO x emissions was achieved using 35% air staging combined with ammonia injection at a NH 3 /NO mole ratio of 0.6:1. The measured ammonia emissions in the flue gas were less than 20 ppm. The present investigation has shown that staged combustion combined with ammonia injection has potential for reducing NO x , emissions, but technical issues such as fouling, corrosion, excess ammonia slippage and the costing implications for this technology remain to be addressed on commercial sized fluidized be combustors.