Namibia Workshop Presentations

Presenter: 
John McNeil

The presentation explores alternative fuels for Combined Heat and Power (CHP).  Aquafuel is a technology company specialising in engine driven combined heat and power.  We can use an internal combustion engine to produce mechanical power or electrical power. When we do this fuel energy is converted to work via heat. Not all of the heat is converted and escapes from the engine from the cooling system and exhaust.  If we capture and make use of the unconverted heat the efficiency ratio of fuel energy conversion to useful work increases. The heat recovered can be used for process steam, building heat, process heat or ‘reversed’ into cooling.  This is known as combined heat and power (CHP) and its use can obviously reduce the amount of CO2 released per unit work. If we use renewable fuels the net CO2 release can be dramatically reduced.  Gas turbines are often used for CHP but tend to be very inefficient at low powers and extremely fuel sensitive.  The following are reciprocating engines as opposed to gas turbines.

• Spark ignited engines. Otto Cycle. These engines when employed in CHP installations usually use natural gas or biogas. A homogeneous charge of fuel and air is compressed and then ignited by a spark. These engines can suffer from early ignition and therefore require high octane fuels. This is the same type of engine used in the gasoline automobile.
• Compression ignition engines. Diesel Cycle. These engines when employed in CHP installations can run on Diesel oil, Bio diesel and larger engines on Heavy Fuel Oil. Air enters the engine and is compressed; fuel is then injected directly into the combustion chamber forming a heterogeneous mixtures of fuel and air. The temperature of the compressed air is high enough to ignite the diesel fuel. Fuels used in this cycle are required to have a high cetane number; the measure of ignition quality. This is the same type of engine used in  diesel cars and trucks.
• Dual fuel compressions ignition engines. These engines use a ‘pilot’ injection of high cetane fuel to ignite a fuel air mixture of natural gas or biogas. This type of engine is quite common in power generation and can be found in trucks an buses.

Aquafuel have developed patented fuel preparation and engine maintenance systems to enable the use of most crude oils and fats and mixtures thereof.  Aquafuel concludes that:

• Renewable fuels are better employed in CHP than in road transport
• CHP will eventually form a very large part of the energy reserve for road transport
• Bio methane is a good CHP fuel if clean.
• Pyrolysis gases are problematic
• Pyrolysis oils are highly problematic. Synthetic bio oils are progressing
• Bio oils and fats are good CHP fuels in their crude form as long as they are correctly applied and are from a sustainable resource
• Ethanol , methanol and butanol are more suited to the road transport industry
• Algal oils have potential if marine
• Algal glycerol has  great potential
• Glycerol has very great advantages as a CHP fuel