Tackling emissions challenges with cleaner, greener engines

Jon Lawson

Paul Dowman-Tucker reveals how to tackle the emissions challenges of today and tomorrow.

Reducing emissions continues to be the most important element of the global climate change agenda, from the National Emission Ceilings Directive (NECD) to the Medium Combustion Plant Directive (MCPD) and other provisions on the horizon.

For example, the UK- and EU-wide MCPD, came in to law from the end of 2018, placing considerable emissions reduction targets for users of engines and generator sets (gensets) with a combined thermal input up to 50MW. Due to this legislation, and shifting attitudes towards diesel fuelled gensets, there has been a large rise in the use of gas fuelled gensets.

Although this has helped many get closer to the MCPD’s nitrous oxide emissions (NOx) targets, the rise in gas gensets has caused a rise in unburnt hydrocarbon (UHC) emissions, including methane, which has a greenhouse gas effect 25-100 times that of CO2.

In much the same way as the increase in diesel gensets led to regulation around NOx, the rise in gas gensets has put the need for tighter UHC emissions regulations on the horizon.

Whether you are tackling the challenges of today with diesel, or those of tomorrow for gas, the need for solutions has never been higher.

A proactive solution

It would be extremely costly, time-consuming and even wasteful for all users of gensets to replace or modify their diesel and gas engines to achieve these new targets. Likewise, if we shift the focus to OEMs, they face considerable burdens around cost, time and resources for R&D of new technologies to reach these targets, along with installation of any solutions.

These are highly challenging targets on all sides and it’s clear a solution is needed that fits the resources of all parties.

Bowman Power uses technology to enable its customers to meet the emissions challenges of today and those on the horizon. Its Electric Turbo Compounding (ETC) system converts waste exhaust energy into electrical power, helping to improve power density and fuel efficiency.

How it works

Bowman’s ETC system combines a turbo generator (TG) with a power electronics (PE) unit.
Initially, exhaust gas from the engine, with high temperature and pressure, flows into the TG. Within the TG, stationary nozzle guide vanes then direct the flow toward rotating rotor blades downstream. The flow of exhaust gas passes over the turbine blades and the energy within the gas (high temperature and high pressure) is transferred to the rotor. The gas then exits the TG at close to ambient pressure, still at a relatively high temperature. The spinning rotor turns a shaft, which then turns an alternator to produce a non-stable AC current, that is exported to the PE unit. This AC input current is converted to DC within the PE before final conversion to three phase AC grid quality (50/60Hz) output.

This combination of high-speed electrical machines (HSEMs) with power electronics to drive and control them, is an innovative approach that has achieved over 22 million run hours across 800 installations.

Emissions reductions

By improving the efficiency of diesel and gas-fuelled reciprocating engines, Bowman has reduced CO2 emissions by over 300,000 tonnes globally.

In addition, by reducing the scavenging pressure in the engine cylinders, the firm has been able to almost entirely eliminate fuel short circuiting (or methane slip) and reduce the release of non-combusted fuel to the exhaust on gas-fuelled engines. This has led to an up to 40% reduction in unburnt hydrocarbon emissions, together with fuel savings. The increase in power generated and fuel saved by the ETC system considerably exceeds any losses in engine efficiency due to the reduction in scavenging pressure.

When all emissions are taken in to consideration, Bowman’s systems can achieve up to a 23% reduction in CO2 equivalent greenhouse emissions of gas fuelled engines/generators over a 20-year time horizon (based on data from the Intergovernmental Panel on Climate Change, IPCC 2007 – AR4).

Integration and payback

Through extensive R&D, Bowman has been able to reduce the cost of its technology by 50% over the past three years and create a third generation of the product that supports a wider range of engines.

As ETC technology can be retrofitted to the majority of engines, from 150kW to 2.5MW range, with specialist solutions available up to 20MW, it allows the firm’s customers to achieve emissions targets and increase output without large investment in new engines or costly engine modification.

In addition to the environmental benefit, payback has been achieved as quickly as 12 months, making this a very cost-effective solution.

From day one Bowman has set out to make the energy mix greener by enabling more efficient and cleaner operations with fossil fuels where it is necessary to use them. The company is not aware of any other technology that can reduce emissions at this level and that offers the same fast payback, simple installation and efficiency uplift.

Already in use across several sectors globally and with partnerships being pursued to work directly with OEMs, the future for the ETC technology looks incredibly optimistic.

In addition to ETC, Bowman is developing further HSEMs, including e-Turbo and e-Compressors for the on-highway market, that will continue to build on its legacy of reducing emissions and increasing efficiency.

Paul Dowman-Tucker is CEO of Bowman Power.

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