Hasril Hasini

An improved solar PV system for Malaysian rural electrification part I: Design and testing of solar PV with tracker and reflectors

This paper is the first of a set describing the investigation on an improved solar photovoltaic (PV) system for specific application in Malaysian rural electrification. The application will be applied as part of the renewable energy solutions for the underserved communities with particular emphasis given to local and native villages in Sabah and Sarawak. The paper presents recommended design and testing of a stand-alone PV system carried out to confirm its effectiveness as compared to the conventional solar PV system. In order to achieve a reliable long-term performance of the PV system, reflectors and solar tracker are adopted into the system and its performance characteristics are carefully investigated via experiment. The efficiency and performance of the new solar PV system were calculated and compared with the conventional one. It has been demonstrated that the solar PV system with solar tracker and reflectors showed good performance improvement as compared to the conventional module.

Impact of tangential burner firing angle on combustion characteristics of large scale coal-fired boiler

Combustion characteristics in large scale boilers are influenced by a number of factors such as coal properties and burner operating conditions. Burner firing angle for example, will affect the fireball size and locations of heat release which affect the formation of ash slagging in a tangentially fired furnace. In this study, a computational fluid dynamics (CFD) simulation of coal combustion in a tangentially fired 700 MW power plant was developed to investigate the impact of burner firing angles on the flame profile in the furnace. The model was developed based on the two-phase flow model, coal devolatilization, char burnout model, discrete particle tracking and radiation heat transfer. The firing angles were changed by ±5° from the base angle of 43° and 55°. The study shows that firing angles have significant effect on the size of the flame fireball and the concentric fireball arrangement. Increasing the firing angle resulted in a larger fireball size with a region of low temperature at the core of the fireball. The simulation also shows that the flow profile becomes more stable with increasing firing angle, regardless of burner elevations. The results presented in this paper may enhance the understanding the complex relation between burner operating condition such as firing angle on flow patterns and combustion processes in a tangentially fired boilers.

Numerical Modeling of Wet Steam Flow in Steam Turbine Channel

In power station practice, work is extracted from expanding steam in three stages namely High Pressure(HP), Intermediate Pressure(IP) and Low Pressure(LP) turbines. During the expansion process in the LP turbine, the steam cools down and at some stages, it nucleates to become a two-phase mixture. It is well-acknowledged in the literature that the nucleating and wet stages in steam turbines are less efficient compared to those running with superheated steam. With the advent of water-cooled nuclear reactor, the problem becomes more prominent due to the fact that in water-cooled nuclear reactor, the steam generated is in saturated condition. This steam is then supplied to the HP steam turbine which therefore has also to operate on wet steam. One of the tangible problems associated with wetness is erosion of blading. The newly nucleated droplets are generally too small to cause erosion damage but some of the droplets are collected by the stator and rotor blades to form films and rivulets on the blade and casing walls. On reaching the trailing edges or the tips of the blades, the liquid streams are re-entrained into the flow in the form of coarse droplets. It is these larger droplets that cause the erosion damage and braking loss in steam turbine. However, the formation and behaviour of the droplets have other important thermodynamic and aerodynamic consequences that lower the performance of the wet stages of steam turbines.

An improved solar PV system for Malaysian rural electrification part II: Implementation and economic analysis of solar PV system with tracker and reflectors

This paper is the second of a set describing the implementation and economic analysis of an improved solar photovoltaic (PV) system for Malaysian rural electrification. The work was carried out based on a case study in a rural community to replace their diesel-powered generators with the new renewable energy (RE) solutions, with buffer capacity for additional requirements. Based in the extensive tests done on the system, it is proven that the new improved design of solar power system can be implemented as it meets the technical requirements of the project. Considering not only the technical requirement, it is also important to design the implementation and maintenance schedule of the system since the local communities have no or little exposure to this system. With adequate trainings and briefings, the maintenance schedules can help them to get involved in the operation and maintenance of the system. Other than that, the economic value of a PV system is calculated so that it can be compared with other methods of power generation. The details of the implementation of solar power system and its impact to the community are discussed in this paper.

Preliminary theoretical study of the formation and growth of droplets in nucleating flows

This paper describes the preliminary study for the prediction of the formation and growth of water droplets in wet stages of a steam turbine. Emphasis is given towards the determination of suitable methods of calculation of suspended droplets in superheated steam. The one dimensional calculation is applied to a duct where superheated steam is allowed to supercool instantaneously as it enters the duct. At the same instance the formation of droplet embryos begins and subsequently, if the surrounding condition permits, it will grow by collecting its surrounding molecules. This process continue for a limited range of time and stops when the supercooling drops, at which the droplets can no longer survives and begins to evaporate. The accumulation of water droplets increases the level of wetness inside the duct. This mechanism is extremely important in the design and operation of low pressure steam turbine, in particular for the prediction of wet region within the machine.

Analysis of flow and temperature distribution in a full scale utility boiler using CFD

There are currently numerous studies on utility boilers using various in-house and commercial CFD codes. Most of the existing simulations are aimed at the flow and combustion properties inside the furnace and therefore, it usually terminates at furnace exit just downstream the re-heater section before the crossover path. On top of that, the majority of these works were based on coal-fired boiler furnace, which has completely different combustion characteristics as compared to natural gas fired boiler. This paper describes an investigation of the prediction of combustion characteristics and flow pattern in a gas-fired boiler. The emphasis is given towards the analysis of flow pattern and its distribution inside the furnace in a steady-state manner. In this investigation, the flow path is extended so that the rear pass, which normally been ignored is included in the calculation domain. Commercial CFD code, CFD ACE+ was used as a tool to carry out the analysis.

The effect of loading condition on the formation of residual swirl in tangentially-fired boiler

This paper presents an investigation of the behavior of reacting flow in industrial boiler with particular interest given towards the effect of boiler load conditions to the velocity and temperature distributions in the furnace chamber. The map of three-dimensional velocity in the furnace domain is manipulated with appropriate mathematical relations to give a clear and concise representation on the swirl effect under the influence of boiler loading condition. From the investigation, it is clear that the residual swirl formed in the furnace is highly influenced by the loading condition. High load condition results in strong combustion gas velocity and vice versa. As opposed to the velocity magnitudes, it is also interesting to notice that the swirl condition is hardly influence by the loading condition.

Influence of furnace cross section on the flow and velocity distribution in tangential firing furnace

This paper presents an investigation on the influence of different furnace cross sectional configurations on the flow and velocity distribution in a small-scale tangential firing furnace. The flow and combustion of natural gas in three furnaces of different cross section are simulated numerically using CFD. The results show that velocity distribution is non-uniform along the width and depth of the furnace in rectangular furnace while square cross section gives uniform distribution. The effect of furnace cross section on the tangential velocity is more obvious when the length difference of the width and depth of the furnace is larger. The axial velocity is found to be highly influenced by the furnace cross section.

Preliminary investigation on the effects of primary airflow to coal particle distribution in coal-fired boilers

This paper presents an investigation on the effects of primary airflow to coal fineness in coal-fired boilers. In coal fired power plant, coal is pulverized in a pulverizer, and it is then transferred to boiler for combustion. Coal need to be ground to its desired size to obtain maximum combustion efficiency. Coarse coal particle size may lead to many performance problems such as formation of clinker. In this study, the effects of primary airflow to coal particles size and coal flow distribution were investigated by using isokinetic coal sampling and computational fluid dynamic (CFD) modelling. Four different primary airflows were tested and the effects to resulting coal fineness were recorded. Results show that the optimum coal fineness distribution is obtained at design primary airflow. Any reduction or increase of air flow rate results in undesirable coal fineness distribution.

CFD analysis of temperature imbalance in superheater/reheater region of tangentially coal-fired boiler

This paper presents a CFD analysis of the flow, velocity and temperature distribution in a 700 MW tangentially coal-fired boiler operating in Malaysia. The main objective of the analysis is to gain insights on the occurrences in the boiler so as to understand the inherent steam temperature imbalance problem. The results show that the root cause of the problem comes from the residual swirl in the horizontal pass. The deflection of the residual swirl due to the sudden reduction and expansion of the flow cross-sectional area causes velocity deviation between the left and right side of the boiler. This consequently results in flue gas temperature imbalance which has often caused tube leaks in the superheater/reheater region. Therefore, eliminating the residual swirl or restraining it from being diverted might help to alleviate the problem.