DOI: 10.14457/tu.the.2021.69
title: Optimal combustion control of untreated landfill gas via averaging pulse width modulation

description: In Thailand, there have recently been a few small-scale preliminary studies on power generation from landfill gas so as to assess technical feasibility prior to performance of full-scale projects. This paper presents financial analysis of those studies on electricity generation by using an Internal Combustion Engine (ICE), Organic Rankine Cycle (ORC), Stirling Engine (STE). Financial indices, such as levelized cost of electricity, net present value, internal rate of return, and payback period, are determined from actual costs of those studies to produce electricity of the power engines from landfill gas. It is found that all financial indices of ICE are mostly acceptable compared with ORC and STE, although cost of gas preparation and high maintenance in ICE are required. From investigation, this advantage of ICE is because of the highest electricity generation with compactness and wide availability in local market. In turn, the levelized costs of electricity of ICE, ORC, and STE are 0.11 USD/kWh, 0.30 USD/kWh, 0.42 USD/kWh respectively. At present, ICE might be a promising engine until costs of the imported ORC and STE decrease at feasible level of finance.The investment of landfill gas is still have high cost and by products (CH4+CO2). It should has a treatment process before using in the internal combustion engine for generating power. Therefore, this paper will present the external combustion by creating the system of untreated landfill gas. And the most important equipment for controlling this combustion is valve. In control of on–off valves for linear flow characteristics is a challenging design problem due to nonlinearity of valve mechanism and fluidic properties under various operating conditions. In this study, averaging pulse width modulation (PWM) is proposed as a control valve signal by implementing PWM with predetermined duty period so that overflow at the open position and underflow at the closed position are divided proportionately around desired mean flow rates during entire cycle periods. Multichannels in a parallel pattern are implemented to yield linear flow characteristics with higher resolution than a single channel. With pressure and temperature measurements, the volumetric flow rate is determined by an empirical model of flow characteristics across flow control valves at given operating conditions. The experimental results on achieving the desired volumetric flow rate of air under actual flow conditions without a flow meter are presented for viability of the proposed methodology in practical uses.So, the optimizing control valve signal and the combustion control in this experimental are found by using the trial model. Optimal combustion control of untreated landfill gas is proposed for an effective usage and a low-cost solution in waste to energy technologies. Variations of methane concentration in untreated landfill gas over time cause undesired performance of combustors in thermal efficiency and gas emission. In this work, the experimental investigation on variables of combustion process is systematically presented to determine an inherent performance index of a combustor, reflecting actual thermal efficiency and gas emission for optimal control. Those quantitative findings can be implemented via fuzzy logic rule knowledge based approach to combustion control. From the experimental results of a can-type combustor, it is confirmed that the optimal combustion control of untreated landfill gas yields the desired exhaust gas temperature with maximum thermal efficiency and minimum gas emission under varying methane concentrations or changes of operating conditions. The proposed methodology can be generalized to optimal combustion control of untreated landfill gas via the fuzzy logic rule knowledge based approach, which is the most suitable to characteristics of each combustor.