Electricity is a vital resource for modern society, but it also has a negative impact on the environment. Most of the electricity is generated from fossil fuels, which are non-renewable and polluting. There is a need for cleaner and more sustainable alternatives that can meet the increasing demand for power. One of these alternatives is vegetable oils, which are renewable fuels that can be used in diesel engines for power plants.
Vegetable oils are obtained from plants such as soybean, rapeseed, palm, sunflower, and jatropha. They are renewable, biodegradable, and carbon-neutral, meaning they do not add to net greenhouse gas emissions. They are also widely available and can be produced locally, reducing the reliance on foreign oil and improving energy security.
Vegetable oils have a long history of use as fuels for diesel engines, which were invented by Rudolf Diesel in 1900. Diesel engines are commonly used in power generation due to their high efficiency, reliability, and flexibility. They can run on various fuels, including vegetable oils, with minimal modifications.
However, vegetable oils have some limitations that restrict their use as direct fuels for diesel engines. They have higher viscosity and density than diesel fuels, which can cause issues such as poor atomization, incomplete combustion, injector coking, and engine deposits. They also have lower heating value and cetane number than diesel fuels, affecting engine performance and emissions.
To overcome these limitations, vegetable oils can be transformed into biodiesel, a liquid fuel with similar properties to diesel fuel. Biodiesel is made by combining alcohol with vegetable oil, animal fat, or recycled cooking grease in a process called transesterification. Biodiesel can be used as a pure fuel or blended with diesel fuel in any ratio.
Biodiesel has several benefits over diesel fuel and vegetable oils. It has lower viscosity and density than vegetable oils, which improves fuel injection and combustion. It has a higher cetane number and oxygen content than diesel fuel, which improves engine performance and reduces the emissions of carbon monoxide (CO), hydrocarbons (HC), and particulate matter (PM). It also has lower sulfur content than diesel fuel, reducing sulfur oxide (SOx) emissions.
However, biodiesel also has some drawbacks that need to be solved. It has lower heating value and stability than diesel fuel, which can reduce the engine power output and cause fuel degradation. It also has higher nitrogen content than diesel fuel, which can increase the emissions of nitrogen oxides (NOx). Furthermore, biodiesel production requires additional energy and resources that may affect its economic feasibility and environmental impact.
Several studies have been conducted to evaluate the feasibility of using vegetable oils and biodiesel as renewable fuels for power plants based on low and medium-speed diesel engines. Low-speed diesel engines are large two-stroke engines that operate at speeds below 300 rpm. They are mainly used for marine propulsion and baseload power generation. Medium-speed diesel engines are four-stroke engines that operate at speeds between 300 and 1200 rpm. They are used for marine propulsion, peak load power generation, and combined heat and power (CHP) applications.
One of these studies examined the performance of a medium-speed diesel engine running on rapeseed oil. The results showed that rapeseed oil could replace marine gas oil (MGO), the conventional fuel for medium-speed diesel engines, without significant engine modifications or loss of efficiency. The emissions of CO, HC,and PM were reduced by 20%, 30%, and 50%, respectively. However, the emissions of NOx were increased by 10%.
Another study tested the performance of a low-speed diesel engine running on palm oil. The results indicated that palm oil could replace heavy fuel oil (HFO), the conventional fuel for low-speed diesel engines, with minor engine modifications or loss of efficiency. SOx, soot, and CO emissions were reduced by 100%, 40%, and 30%, respectively.
However, the emissions of NOx were increased by 20%. These studies demonstrate that vegetable oils have a high potential as renewable fuels for power plants based on low and medium-speed diesel engines. They can reduce the dependence on fossil fuels and lower the emissions of certain pollutants and greenhouse gases.
Some of the solutions for using vegetable oils as renewable fuels for power plants are:
- Fuel quality: To ensure fuel quality, vegetable oils need to be properly filtered, dried, and stored. They also need to meet certain standards and specifications for fuel properties such as viscosity, density, flash point, cetane number, and heating value. These standards and specifications can vary depending on the type of engine and the application. For example, the International Organization for Standardization (ISO) has developed a standard for marine fuels (ISO 8217) that covers both fossil fuels and biofuels.
- Fuel supply: To ensure fuel supply, vegetable oils need to be produced from diverse and sustainable sources that do not compete with food production or cause deforestation. They also need to be transported and distributed efficiently and safely. For example, some countries have established policies and incentives to promote the production and use of biofuels from local feedstocks. For instance, Brazil has a long history of using ethanol from sugarcane as fuel for vehicles. Similarly, Indonesia has the mandate to blend biodiesel from palm oil with diesel fuel for transportation and power generation.
- Engine performance: To improve engine performance, vegetable oils need to be blended with diesel fuels or additives that can enhance their properties. They also need to be preheated or diluted to reduce their viscosity and improve their flowability. For example, some studies have shown that blending vegetable oils with diesel fuels can improve the engine power output and efficiency by reducing the fuel consumption and increasing the cetane number. Some additives that can be used to improve the properties of vegetable oils include antioxidants, lubricity enhancers, detergents, and cetane improvers.
- Engine emissions: To reduce engine emissions, vegetable oils need to be treated with catalysts or additives that can lower their NOx formation. They also need to be optimized for different engine operating conditions, such as load, speed, and temperature. For example, some studies have shown that using selective catalytic reduction (SCR) systems can reduce the NOx emissions from vegetable oil-fueled engines by up to 90%. Some additives that can be used to reduce the NOx emissions from vegetable oils include urea, water, and ethanol.
In conclusion, using low- and medium-speed diesel engines, vegetable oils are promising renewable fuels for power plants. They can offer environmental and economic benefits over fossil fuels by reducing greenhouse gas emissions and enhancing energy security. However, they also face technical and logistical challenges that must be solved to ensure their feasibility and sustainability. @via sciencedirect.