Mechanical Technology Archive

MechTech talks to Cummins’ Kenny Gaynor, director of power generation for Southern Africa, about the role of diesel, gas and biogas engine-generator sets and hybrid options.

Kenny Gaynor Cummins power generation southern africaAccording to Gaynor, generators have two key uses: for standby power to mitigate against the risks of power outages from a connected supply; and for prime power with an unlimited run time for use in industrial applications where the grid is not readily accessible.

As well as during load shedding, standby power generators are often used in emergency or safety critical situations. “Power is critical for safety in underground mines, for example, where lives depend on electrical power, from the basic siren/alarm system all the all the way to the ventilation, cooling plants and evacuation hoist,” he tells MechTech.

“In hospitals, surgeons cannot continue to operate on a patient if there is no power and patients on life support systems such as dialysis machines won’t survive long if these machines are left without power for any length of time,” he argues.

Cummins offers a range of backup power options, from 8.0 kVA to 3 750 kVA. “We offer open sets for installation in plant rooms or containerised units that can be placed outside shopping malls. For applications along the coast, we can use stainless steel enclosures and, generally, we can engineer a standby power system and its enclosure to best suit the application, the environment and the operating conditions.

Cummins QSV91 natural gas generator setDue to the drought, standby power has become increasingly necessary in hydro-dependant countries north of our borders. Inadequate grid availability in South Africa affects exports to neighbouring countries and drought causes low water flow, so turbines have to be shut down. This is particularly problematic in the dry winter seasons in countries dependant on the Zambezi: Zambia, Zimbabwe, Mozambique, Malawi and Namibia.

“Engine-driven generators for standby and prime use are different, though. A unit used for 600 continuous hours a month has a very different duty cycle than a backup generator that is started several times a month for 200 hours or less of total generation. The specification of the engine and the generator, as well as the power management solution and the cost equations are all very different,” Gaynor points out.

For prime use, Cummins Power Generation offers solutions for people needing a 24/7 supply, typically a remote off-grid mine or a mine under development, for example, “and while diesel power generation is always going to be more expensive than utility power, if access to the grid is unavailable, then there are fewer options other than prime units”.

On the advantages of diesel engines, Gaynor says there is “nothing better for picking up a load”. “Diesel engines are amazing when it comes to absorbing changes in load, either up or down,” he argues.

With the price of diesel at around one US$ per litre, diesel generated power costs somewhere upwards of $0.30 per kWh “And about 73% of this cost can be attributed to the diesel fuel costs, with capex and maintenance accounting for the remaining 27% of the levelised cost of electricity (LCOE).

“The capex and maintenance costs are low but the big issue is running costs due to fuel. This makes prime diesel generators ideal for use in hybrid solutions. We see companies using solar during the day to reduce the fuel costs, with the diesel being used overnight. Solar technology is now quite sophisticated. Management systems can predict when the solar output is about to drop due to cloud cover, for example, and the diesels can be started in time to prevent power dipping. The diesels ramp up in sync with the solar coming off and the load doesn’t see any change in the supply,” he informs MechTech.

“These hybrid system could see some 20% savings on diesel fuel costs, which has a huge impact on the levelised kWh cost. Almost all solar PV costs are capex –which can be recouped very quickly – and in term of running costs, even the maintenance of solar systems is minimal, limited to cleaning.

In Africa, however, particularly in North and West Africa, cloud cover can be a big problem, causing the diesels to come in more often than they would in sunnier places,” Gaynor says, adding, “the cost of solar has decreased significantly in recent times, though, making hybrid diesel-solar solutions very attractive for mining operations that are off-grid”.

This also applies to cell phone towers in rural Africa, which use generators, battery storage and PV panels in similarly managed hybrid combinations. “The generator charges the batteries at night while the solar PV charges them when the sun is shining, with the batteries supplying the direct load,” he explains.

As is now common with modern control and power management technology, remote monitoring capabilities are readily available and built into Cummins power solutions. “When called to look at generators that aren’t working, we often find that a security guard has borrowed the battery to start his car or the fuel tank has run empty. These trivial issues and common and remote monitoring can easily be used to overcome them.

“On a level above this is engine diagnostics. Sensors are installed in all modern engines and this information is ideal for preventative maintenance, to alert plant managers to engine problems before they cause serious damage,” he tells MechTech.

On the emissions side, Gaynor says that Cummins is ahead of the curve. “Internationally, we supply Tier IV diesel engines, but the issue in Africa is fuel quality, so we are still supplying Tier III systems. We design and manufacture our own emissions and filtration systems, which can easily be incorporate into static backup or prime generation plants. These do require some routine maintenance, though, and in very remote areas, even changing a filter can be difficult,” he suggests.

In the past, a diesel engine designed for other applications would be used for a generator. But nowadays, with our QSK95: 3750, for example, both the engine and the generator are designed from the ground up to suit the specific needs of power generation.

“The loads and acceleration ranges required for generation are very different to transport needs. A mine truck might go from being empty to carrying 200 t when loaded and the speed, rpm and torque ranges are wide. For generation applications, the operating rpm range can be narrowed and held relatively constant for better optimisation of fuel efficiency, reliability and longer maintenance intervals,” he explains. “The power density of generators is also high and they need to be able to ramp electricity generation up or down from full load to zero in less than 10 seconds.

“Footprint is also important, as are sound levels. Our units produce 75 dB at 1.0 m and down to 62 to 65 dB at 7.0 m, but enclosures can be used to dampen this right down to below 55 dB, which is the standard specification for hospitals,” he adds.

Gas power generation

Natural gas and biogas engines are an increasingly viable alternative to diesel gensets, particularly for combined heat and power applications. “Gas engine exhausts run hotter than diesel equivalents, by about 200 °C. So by passing the exhaust gas through a heat exchanger, a second and free source of energy in the form of heat becomes available. There is an ideal application in hospitals, for example, where substantial amounts of hot water are needed, as well as prime and uninterrupted electrical power.

“Most hospitals are already using gas for their boilers. We like to redirect that gas into an engine to produce both heat and power. In so doing, we can often take the hospital off-grid without having to use substantially more fuel,” Gaynor explains, adding: “We have done numerous studies and the cost balance is there. It is a little marginal at the moment but with rising grid-based tariffs, this solution is becoming increasingly attractive.”

Piped gas is ideal as it overcomes the need for onsite diesel tanks or regular deliveries but, where a gas infrastructure is not available, compressed natural gas from tanks can also be used, with the trucking cost being similar to diesel. “From a fuel cost perspective, the $0.30 per kWh LCOE for diesel can be brought down close to the $0.20 mark, obviously driven by local gas costs. In Nigeria, where engine generators are routinely used for prime generation, we are seeing price reductions from 30 cents (US) to perhaps 18 cents, when switching from diesel to gas. In addition, the high quality CO2 in the exhaust stream can offer a third bite of the cherry for bottling, food and beverage companies,” Gaynor points out.

The direct efficiency of a gas engine-driven generator is around 40 to 42% “but a further 45% can be added to that by beneficiating the heat. That allows these systems to achieve overall efficiencies of more than 80%, which is remarkable for an energy generation system driven by an internal combustion engine,” he tells MechTech.

Another opportunity for CHP systems is for data centres, where cooling dominates the load profile. “Using absorption chillers for the HVAC systems of data centres, the exhaust heat from the gas engines can be used instead of electricity to meet the cooling demand. The data centre can then be taken off-grid in a very cost effective and convenient way – and we are sure to see more and more data centres using this technology,” Gaynor says.

Cummins offers gas-based generation solutions from 25 kVA to 2 000 kVA, with the 16 cylinder, 91 litre QSV91 system being the upper-end flagship. “We have the smaller solutions too, though, for small offices or remote clinics, which often only need 25 kW,” he adds.

Moving away from natural gas, Gaynor sites the use of gas engine systems fuelled by biogas generated from municipal waste: from landfill sites or sewage works. “Designed in 1970s and 80s, increasing urbanisation has created management problems for sewage plants. Biogas-fuelled CSP systems offer an excellent opportunity to exploit the waste creating the problem,” believes Gaynor.

For sewage, there are two opportunities to extract biogas (methane) for a generator, first directly off the liquid and, second, by gasifying the solid sludge – the exhaust heat from the gas engine being an ideal heat source for drying the sludge.

Not only does this enable a sewage works to be taken off grid, making the plant self-sufficient, it can offer opportunities to sell power to nearby housing or industrial estates. “On urban landfill sites where space is constrained, a methane plant can be installed to extract the methane from buried organic waste. This can be used by a gas engine to produce heat and power for sale into businesses and communities.

“This is a perfect example of how thinking a little further about our problems can create new opportunities to beneficiate our resources,” Gaynor argues. “These need not be mega plants. Plants of 20 to 100 kW can be cost effective and the technology is available and relatively simple,” he adds.

Long term, power generation from biogas also offers renewable energy opportunities: “Cactus is an excellent feedstock for biofuel production, offering opportunities for mines to better engage with and support surrounding rural communities. By planting and harvesting cactus, agricultural jobs are secured with the harvest being sold to a biofuel producer. The fuel is then sold to a power plant, for credits or kWh, and the power used to create growth opportunities in the community: bakeries, Internet cafés, shops or small industries,” Gaynor suggests.

Concluding, he says that generators are currently often seen as a necessary ‘grudge purchase’. “Companies know that they need them but often make the mistake of seeing them as a once-off purchase at the minimum cost possible. Backup service and maintenance is very important, though. Are parts available, are the products being properly supported and serviced and is anyone available for callout should problems be experienced?

“If the power goes off, can you rely on the purchased generator to supply the backup power? The lowest cost options is seldom going to be the safest one,” he warns.

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