Abstract: The development of transport systems has negative
impacts on the environment although it has beneficial effects on
society. The car policy caused many problems such as: - the
spectacular growth of fuel consumption hence the very vast increase
in urban pollution, traffic congestion in certain places and at certain
times, the increase in the number of accidents. The exhaust emissions
from cars and weather conditions are the main factors that determine
the level of pollution in urban atmosphere. These conditions lead to
the phenomenon of heat transfer and radiation occurring between the
air and the soil surface of any town. These exchanges give rise, in
urban areas, to the effects of heat islands that correspond to the
appearance of excess air temperature between the city and its
surrounding space. In this object, we perform a numerical simulation
of the plume generated by the cars exhaust gases and show that these
gases form a screening effect above the urban city which cause the
heat island in the presence of wind flow. This study allows us: 1. To
understand the different mechanisms of interactions between these
phenomena.2. To consider appropriate technical solutions to mitigate
the effects of the heat island.
Abstract: Palm kernel shell is an important bioenergy resource
in Thailand. However, due to elevated alkali content in biomass ash,
this oil palm residue shows high tendency to bed agglomeration in a
fluidized-bed combustion system using conventional bed material
(silica sand). In this study, palm kernel shell was burned in the
conical fluidized-bed combustor (FBC) using alumina and dolomite
as alternative bed materials to prevent bed agglomeration. For each
bed material, the combustion tests were performed at 45kg/h fuel feed
rate with excess air within 20–80%. Experimental results revealed
rather weak effects of the bed material type but substantial influence
of excess air on the behavior of temperature, O2, CO, CxHy, and NO
inside the reactor, as well as on the combustion efficiency and major
gaseous emissions of the conical FBC. The optimal level of excess air
ensuring high combustion efficiency (about 98.5%) and acceptable
level of the emissions was found to be about 40% when using
alumina and 60% with dolomite. By using these alternative bed
materials, bed agglomeration can be prevented when burning the
shell in the proposed conical FBC. However, both bed materials
exhibited significant changes in their morphological, physical and
chemical properties in the course of the time.
Abstract: Catalytic combustion is generally accepted as an environmentally preferred alternative for the generation of heat and power from fossil fuels mainly due to its advantages related to the stable combustion under very lean conditions with low emissions of NOx, CO, and UHC at temperatures lower than those occurred in conventional flame combustion. Despite these advantages, the commercial application of catalytic combustion has been delayed because of complicated reaction processes and the difficulty in developing appropriate catalysts with the required stability and durability. To develop the catalytic combustors, detailed studies on the combustion characteristics of catalytic combustion should be conducted. To the end, in current research, quantitative studies on the combustion characteristics of the catalytic combustors, with a Pd-based catalyst for MCFC power generation systems, relying on numerical simulations have been conducted. In addition, data from experimental studies of variations in outlet temperatures and fuel conversion, taken after operating conditions have been used to validate the present numerical approach. After introducing the governing equations for mass, momentum, and energy equations as well as a description of catalytic combustion kinetics, the effects of the excess air ratio, space velocity, and inlet gas temperature on the catalytic combustion characteristics are extensively investigated. Quantitative comparisons are also conducted with previous experimental data. Finally, some concluding remarks are presented.
Abstract: The experimental results on combustion of rice husk
in a conical fluidized bed combustor (referred to as the conical FBC)
using silica sand as the bed material are presented in this paper. The
effects of excess combustion air and combustor loading as well as the
sand bed height on the combustion pattern in FBC were investigated.
Temperatures and gas concentrations (CO and NO) along over the
combustor height as well as in the flue gas downstream from the ash
collecting cyclone were measured. The results showed that the axial
temperature profiles in FBC were explicitly affected by the
combustor loading whereas the excess air and bed height were found
to have minor influences on the temperature pattern. Meanwhile, the
combustor loading and the excess air significantly affected the axial
CO and NO concentration profiles; however, these profiles were
almost independent of the bed height. The combustion and thermal
efficiencies for this FBC were quantified for different operating
conditions.
Abstract: Because of importance of energy, optimization of
power generation systems is necessary. Gas turbine cycles are
suitable manner for fast power generation, but their efficiency is
partly low. In order to achieving higher efficiencies, some
propositions are preferred such as recovery of heat from exhaust
gases in a regenerator, utilization of intercooler in a multistage
compressor, steam injection to combustion chamber and etc.
However thermodynamic optimization of gas turbine cycle, even
with above components, is necessary. In this article multi-objective
genetic algorithms are employed for Pareto approach optimization of
Regenerative-Intercooling-Gas Turbine (RIGT) cycle. In the multiobjective
optimization a number of conflicting objective functions
are to be optimized simultaneously. The important objective
functions that have been considered for optimization are entropy
generation of RIGT cycle (Ns) derives using Exergy Analysis and
Gouy-Stodola theorem, thermal efficiency and the net output power
of RIGT Cycle. These objectives are usually conflicting with each
other. The design variables consist of thermodynamic parameters
such as compressor pressure ratio (Rp), excess air in combustion
(EA), turbine inlet temperature (TIT) and inlet air temperature (T0).
At the first stage single objective optimization has been investigated
and the method of Non-dominated Sorting Genetic Algorithm
(NSGA-II) has been used for multi-objective optimization.
Optimization procedures are performed for two and three objective
functions and the results are compared for RIGT Cycle. In order to
investigate the optimal thermodynamic behavior of two objectives,
different set, each including two objectives of output parameters, are
considered individually. For each set Pareto front are depicted. The
sets of selected decision variables based on this Pareto front, will
cause the best possible combination of corresponding objective
functions. There is no superiority for the points on the Pareto front
figure, but they are superior to any other point. In the case of three
objective optimization the results are given in tables.