HMI SIMULATION OF BIOGAS HANDLING OF GAS ENGINE SYSTEM Effect of Temperature on Biohydrogen Production from Palm Oil Mill Effluent (POME) Fermentation

1) 1) 1) 1) 2) Nugroho Adi Sasongko , Anton Rahmawan , Hartadhi , Arga Febriantoni , WinaldhaErza N.H , 2) 2) M Taufiqi Arrais , and Agus Rochmansyah Pusat Teknologi Sumberdaya Energi dan Industri Kimia Agency for The Assessment and Application of Technology (BPPT) Kawasan PUSPIPTEK Serpong Tangerang Selatan 15314 Sepuluh NopemberTechnology Institute (ITS), Surabaya Email: nugroho.adi@bppt.go.id


INTODUCTION
Palm Oil Mill Effluent (POME) can endanger the environment,since POME is categorized as a very high contaminating wastewater that can contains a biochemical oxygen demand (BOD) of 25,000 mg and chemical oxygen demand (COD) of 69,500 mg (Najafpour, 2006). Since raw POME normally is discharged at 80-90 °C, therefore several researchers reported that treatment of POME can be done whether in mesophilic or thermophilic conditions (Zhang, 2008 ;Mustapha, 2003).
Production of biogas from POME is widely known by using either anaerobic or aerobic digestion (Akobi, C. et al., 2016).The typical production process is as illustrated in Figure 1. Anaerobic digestion is a process where organic materials are decomposed in a condition where there is no oxygen present and useful biogas is produced, simultaneously. There are three stages of reactions involved in anaerobic digestion and then, its potential of treating wastes while producing renewable energy become biogas. The first stage is hydrolysis, followed by acidogenesis and lastly methanogenesis (O-Thong, et al., 2016 ;Yuzir A. et al., 2012).
Gas engine is a spark ignition combustion that uses gas fuel, in which the mixture of air and gas is compressed and ignited with spark plug. Biogas could be an alternative fuel to replace biomass fuel and diesel.Biogas is typically composed of 50-75% methane (CH ), 25-45%, carbon dioxide 4 (CO ), and trace amounts of other gases (Rahayu, 2 dkk., 2015 ;Youngsukkasem, et al., 2013 ;Yunus, dkk., 2015).
Gas engine usually used fossil fuel and now gas engine can use biogas from result POME processing.
Beforehand, POME is treatedwith some processes, one of which is separation process from unnecessary substances in the scrubber system,water content separation with biogas in the dehumidifier system, and distribution of gas by blower to gas engine by blower system and finally the gas engine will convert the mechanical energy to electrical energy.All of those processes starting from bioscrubber system until supplying biogas to a gas engine is called gas handling.Different blends of biogas with methane or propane and hydrogen additions are usedaccording to the gas engine requirement which is presented in Table 1

MATERIALS AND METHODS
The flow chart in Figure 2explains biogas processing steps, especially on gas engines. A gas engine is a combustion process that converts biogas into electrical energy. The gas engine process starts when the gas and liquid separation results in the scrubber (SB-301), if it has not produced gas and there is still a lot of content in liquid form, it will be back to the CSTRtank and reprocessed continuously. But if the gas has been produced, then it will be distributed to the dehumidifier and analysed by analytical transmitter whether the gas content is in accordance with specification of gas engine specifically designed for biogas. If the gas produced is not in accordance with the specification, the gas will be discarded and burned in flares, but if the gas produced is in accordance with the gas engine specification, then the blower will automatically turn on and open the gas channel so that it can be directly injected into the gas engine as fuel.

HMI,Process System and Logic Diagram
In the bio-scrubber system as shown in Figure 3, gas from the SC2valve enters the SC2 pipe and goes into the scrubbersystem. In scrubbersystem,the temperature and pH of the gas will be purified to reduce H S levels by flushingwater 2 which will convert H Sto SO the temperature 2 4 0 inside the scrubber must be in the range of 40-50 C and pH between6.5 -7.5 after the methane gas is lowered the gas will enter the GH 21 and GH 22 pipes and then enterthe gas holder. In the dehumidifier system as shown inF igure 4, water content of biogas will be reduced through cooling process.Before entering gas dehumidifier, the biogas must meet requirements thatH O must 2 be below 80%, H S must be below 2000 ppm, CH 2 4 must be below 60% and the pH must be between 6.5 to 7.5.
Gas handling system as shown in Figure 5 will direct the gas with reduced water content from dehumidifier to enter the gas holder. Gas in the gas holder will be pumped to the gas engine as fuel by the blower system. If the system detected excessive pressure in the gas holder, the valve (Valve 2) to flaring system will then open and direct the gas to flaring system. Figure 6 show that there are 5 while loops in the logic diagram,eachwhile loops has different function in value change box the function for hyperlinking and launching the program simulation.  There are 4 led indicator in the dehumidifier logic diagram, the led indicator will show green colour if the gas from bio-scrubberis suitable with all the gas components requirementand the blower will purify the gas to remove the water content. Eachgas components havespecific requirement for content and level, it can be less than or higher than or in the midst of. Also, this logic diagram is using basic logic gates, especially AND. Because in the dehumidifier, if one gas component not suitable with the requirement, the blower will not activate and the gas will be directed back to the biorubber.
There are 2 LED indicator in the scrubber logic diagram.The led indicator will show green and red colour, Green LEDs indicates that the biogas has entered the scrubber is in accordance with pH level requirement, if the pHlevel is appropriate then the LED will turn on the indicator to enter the gas engine.Red LED indicator indicates no biogas supply goes to the gas engine because the biogas will be looped once more into the scrubber for treatment repetition.If after treatment it does not show the pH level that matches gas engine specification, the biogas will be directed toflaring systemand LEDindicator on the flaring systemwill be turned on. Many indicators are contained in the gas engine diagram block. Because in fact there are many parts of the engine that must be continuously monitored. The block diagram above is a simple example that has been made in part from the overall engine monitoring system. Part of the monitoring system is specific fuel consumption of the engine during operation. Another is input voltage fromPLN whichis displayed withaims to compare the supply voltage of PLNand the voltage produced by the gas engine generator. Then there is frequency indicator, engine battery voltage, and of course the engine speed (RPM). In addition, there will be a graph of engine vibration, engine oil control, power factor(PF), gas engine display, blower display and other supporting displays that can be added as needed.

Gas Engine
Gas engine is a spark ignition combustion engine that uses gas fuel, in which the mixture of air and gas is compressed and ignited with spark plug.     The experiment result showed that, process of POME can be processed to produce biogas fuel.