Zainal Zakaria

The effect of surrounding temperature on liquefied petroleum gas behaviour during exhaustion process

Liquefied petroleum gas (LPG) is considered to be a cleaner fuel because it has less impact on air quality. However, the potential benefit of LPG usage in domestic or residential sectors in Malaysia is hampered by LPG residue in cylinder. A few critical factors, such as LPG composition, exhaustion rate and surrounding temperature, have been identified to significantly contribute to the LPG residue problem. The present study will only report the effect of surrounding temperature on the behaviour of LPG inside the storage cylinder during exhaustion process. The investigation was experimentally carried out at the surrounding temperature of 10°C to 35°C. The results show that LPG exhaustion operation at the surrounding temperature of 25°C or higher exhibited significant temperature and pressure profiles which explained a considerable reduction of the LPG residue. Radial and axial thermal distribution analysis inside the cylinder indicates that sensible heat needed for evaporation process was derived mainly in the axial direction at the regions adjacent to the internal wall.

Tomographic image reconstruction of monitoring flaws on gas pipeline based on reverse ultrasonic tomography

The capability of a technique to reconstruct a tomographic image of flaws existence on gas pipeline via reverse ultrasonic tomography is presented. The ultrasonic tomography system is developed to monitor flaws circumferentially on pipeline with contactless measurement of distance from sensors to the pipe. In oil and gas industry, the applications of ultrasonic tomography technique for flaw detection in pipeline are limited as this technology is still in its infancy. The design of the ultrasonic tomography system consists of ultrasonic sensing system, data acquisition and image reconstruction system. A reflection mode of ultrasonic sensor is used where the output ultrasonic signal reflected from the pipe to the sensor is acquired. The collected data will be used in image reconstruction system to visualize the image. In image reconstruction process, a linear back projection algorithm is used in order to reconstruct the image of the pipe profile with flaws existence. The back projection algorithm is derived by the mathematical relationship of forward and inverse problem. This reconstruction algorithm is implemented in Matlab software to analyze the performance of the technique for different projection and arrays. Through the simulated result, the reconstructed image based on four projections is found to be less smeared compared to the image based on two projections. The effect of aliasing on the image is also reduced as the number of projection is increased. Several images of pipe with flaws existence are reconstructed based on four projections, with 7 × 7 arrays of pixels and twenty-eight of ultrasonic sensors.

Gas reticulation optimisation for domestic sector in Malaysia

Gas distribution has become increasingly important in Malaysia as most of the new housing areas have installed this piping system. A gas network analysis and design computer program with the determination of coincident factor has been developed to optimise the gas distribution system. The optimum and practical gas coincident factor are determined from gas consumption data of several residential areas. From that data, an analytical coincident factor equation has been produced. The developed computer program is used to optimise the existing and future expansion of gas distribution system. The steady state gas network is solved using the Newton-Raphson method due to its fast convergence characteristics. Besides that, the design of a new gas distribution system will be optimised through the use of the developed computer program. Some case studies have been done in order to compare the computed optimisation method with the current method used by gas utility company in Malaysia. [Received: January 23, 2009; Accepted: October 5, 2009]

Batch fermentation of bioethanol from the residues of elaeis guineensis: Optimisation using response surface methodology

In oil palm industry, large quantity of oil palm trunk (OPT) and palm oil mill effluent (POME) are generated. These residues are not fully utilised. They are served as wastes, which lead to serious environmental pollution. Realising that OPT sap contains high glucose concentration while POME contains essential nutrients required by microorganisms for growth, in this study, bioethanol was produced from OPT sap and POME by Saccharomyces cerevisiae in shake flasks culture. OPT sap was used as carbon source, and POME was utilised as nutrient supplier for the fermentation process. To obtain the optimum ratio of OPT sap to POME, inoculum size, initial pH, and incubation time for maximum bioethanol yield, response surface methodology (RSM) via face centred central composite design (FCCCD) was employed. The experimental data for glucose consumption, bioethanol yield, and biomass growth were fitted to polynomial equations and analysed. The quadratic models were employed to fit the data. The optimum bioethanol fermentation conditions were as follows: OPT sap to POME ratio of 63 : 37, inoculum size of 4.3 vol%, initial pH of 8.0, and incubation time of 118 h. Under these conditions, the expected bioethanol yield is 0.453 g/g. To evaluate the accuracy and validate the results, five additional runs were carried out at the optimum point. It was found that the range of bioethanol yield within 95 % confidence level was 0.448 - 0.457. It can be concluded that there is no difference between the experimental values and the predicted data within 95 % confidence level since the predicted data were within the range.