The more efficient the equipment, the greater the benefits or profits that can be obtained. This includes equipment for biochar production, namely pyrolysis. The more efficient the pyrolysis equipment, the cheaper it will be to produce biochar but also produce development products. An example is the use of byproducts from the pyrolysis process such as syngas, biooil, pyroligneous acid and excess heat. Harvesting or utilizing energy from waste heat sources that would normally be wasted is also part of efficiency as well. A number of products that can be used for energy production can be used for electricity production, namely syngas, biooil and excess heat. But there are a number of technologies for producing electricity, so which one do you choose?
A. Gas Engine
Gas engines such as the GE Jenbacher are commonly used to produce electricity from biogas. Biogas, which is a product of bioprocess, has a very dominant methane gas content, while syngas from pyrolysis, which is a thermal process, contains only a small amount of methane and more hydrogen (H2) and carbon monoxide (CO), this means that gas engines are not suitable for producing electricity from syngas pyrolysis. Apart from being suitable for biogas, gas engines such as the GE Jenbacher are also suitable for natural gas, which also contains methane gas.
B. ORC (Organic Rankine Cycle)
The main difference between the Organic Rankine Cycle (ORC) and the ordinary Rankine cycle lies in the working fluid and the temperature of the heat source used. ORC was specifically designed as a modification of the conventional Rankine cycle. The difference with the ordinary Rankine Cycle which uses steam from the boiler as the working fluid which is widely used in large capacity coal powerplants, the ORC uses a working fluid in the form of an organic fluid which has a low boiling point such as hydrocarbons or refrigerants. This low boiling point means that you can use a heat source whose temperature is not too high, such as waste heat or residual heat and so on.
And because there are many organic fluids available, selecting organic materials as suitable working fluids for ORC is no less important. In fact, the choice of working fluid for the ORC generator is very crucial because it affects thermodynamic efficiency, operational costs and safety aspects. The main factors considered are the thermophysical properties of the fluid, compatibility with the heat source, environmental impact, and commercial availability (economic aspects). So the selection of ORC fluid must balance energy efficiency, safety, environmental impact and cost.
Waste heat from pyrolysis can be recovered and used for electricity production with this ORC. Likewise, pyrolysis byproducts that can be used as energy sources are excess syngas and bio-oil. The excess syngas and bio-oil are used as fuel and the heat is used as an energy source for the ORC generator. Basically, the selection of an ORC power plant is based on electricity needs and available energy sources.
For small electricity needs, namely in the range of 0.5 MW - 10 MW and low temperature energy sources, namely those whose temperature is below 350 C (low to medium temperature range (80 C - 350 C)), then the choice of ORC is suitable. As a comparison, steam turbines require temperatures well above 400 C and a power output of 10 MW to above 1,000 MW (as in coal-fired power plants or nuclear power plants). But why do almost all palm oil mills (CPO / crude palm oil mills), even though their electrical power production is small or an average of less than 5 MW, still use steam turbines? For an explanation, read here.
The application of an Organic Rankine Cycle (ORC) generator as waste heat to power (WHP) from the pyrolysis process is a very effective combination to increase the total energy efficiency of the system (co-generation). And modern pyrolysis units are widely used in continuous system biomass pyrolysis, namely for biochar production, which work autothermally or self-sustainably, so it is possible that the pyrolysis unit can also operate independently from the electricity generator from the ORC. This means it will reduce operational costs, because the electricity to run electric motors, pumps and so on comes from its own production. In other words, the pyrolysis unit operates independently without depending on the electricity network or PLN (Indonesia state owned company). From a climate perspective, these conditions are ideal, because the energy source comes from renewable sources (carbon neutral) and if biochar is used for carbon sequestration it means it is carbon negative. Optimizing the system so that it produces an optimal and profitable configuration is the task of engineers.
An American company, namely Quonset Soil Solutions, LLC in Rhode Island, has recently successfully installed an ORC unit to harvest waste heat from their pyrolysis unit with a capacity of 1.8 MW. Apart from that, several pyrolysis units in Europe are also reported to be using ORC with a smaller capacity. These successes will inspire and the installation of ORC units as part of biochar production with (slow) pyrolysis will continue to grow.
Conclusion:
-The ORC system is highly recommended for continuous scale pyrolysis plants (not small batch types) because it is able to convert heat pollution (waste heat) into valuable electrical energy assets constantly. ORC operations are environmentally friendly and support decarbonization targets.
-The ORC generator from waste heat pyrolysis is an efficient, safe and sustainable solution for generating electricity from waste heat energy (residual heat). This technology is also ideal for various industries that produce intermediate heat, so that energy is not wasted.
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