Waste energy: From recovery to management

Waste energy

A simple configuration of waste energy providers and users reduces complexity in Ulmatecy’s waste heat recovery system

As ship owners and operators face the need for increasing efficiency, waste heat recovery is becoming a more attractive proposition. And a new system from Ulmatec Pyro promises a one-stop solution for a range of other water systems. Gavin Lipsith reports.

With the step changes in installed power required by the Energy Efficient Design Index (EEDI), many industry observers suggest that waste heat recovery will play a major role in achieving these reductions. According to some estimates, only 30-40% of energy produced by ships’ engines is used efficiently, with the remainder disappearing as heat through exhaust gas and engine cooling water. In recent years several suppliers have attempted to recapture this energy for applications across vessels.

Mitsubishi Heavy Industries’ (MHI) Waste Heat Recovery System (WHRS), which converts heat from exhaust gas, was first launched in 2010. It now boasts an installed base of 64 vessels, with orders for a further 34 – including 11 new mega-containerships on order from Maersk and under construction at Daewoo Shipbuilding & Marine Engineering. In total Maersk has ordered 69 of the systems.

Conventional waste-heat recovery systems for a main diesel marine propulsion engine supplies electricity to a ship using an exhaust gas economizer and a steam turbine. MHI’s unit consists of a conventional combined system with a gas economizer, a steam turbine and a power turbine (gas turbine) utilising a portion of the exhaust gas, and an automatic clutch.

The power turbine is coupled with the steam turbine through the automatic clutch to drive a generator. The rotating torque of the power turbine is added to the steam turbine to drive the generator. When the total electricity demand of the ship is below the full capacity of the heat recovering generator, the steam system takes the main role with complementary power support from the power turbine.

In total MHI claims that its system can increase the efficiency of marine engine plant by 8-10%. Running on exhaust gas from a marine diesel engine with a maximum continuous rating of 45,740kW at 78rpm, the generator can provide up to 4,000kW at 1,800rpm.

MHI was also involved in the development a more recent waste heat system, launched last year by US-based Calnetix Technologies. As reported in detail last month, the Hydrocurrent system can produce up to 125kW of power for the ship’s electric load from heat recovered out of the engine’s jacket water. The system, which operates using an organic rankine cycle (ORC) heat recovery process, is claimed to be able to generate electricity from water temperature as low as 80°C, below that needed for other systems.

The Hydrocurrent ORC module is a closed-cycle evaporator-condenser phase-change loop, using an organic fluid that has a very low boiling point. The fluid is pumped through an evaporator that pulls heat from the engine’s jacket water. The superheated vapour is expanded across Calnetix’s Thermapower unit, an integrated power module developed by Calnetix.

Another company seeking to mobilise waste energy – both from exhaust gas and engine cooling water – is Norway-based Ulmatec Pyro. The company launched its Pyro waste heat recovery system in 2011 and has so far sold 80 systems, to what managing director Jan Petter Urke describes as ‘major players’ in the market. Maersk have eight systems and Bourbon twenty.

The Pyro system is based on a primary thermal fluid circuit comprising flow and return pipes and a circulating pump module. The thermal fluid is normally a water-glycol mix, and it is pumped around the circuit at a controlled pressure of up to 3 bar, depending on the type of vessel. Pyro systems do not need to use steam to create electricity, running at less than fluid boiling point.

This circuit provides the means for connecting the sources of energy – primarily engine exhausts, jacket cooling Maersk , turbocharger intercoolers and lube oil coolers – to the systems requiring heat. Suppliers and consumers are connected as parallel links between the flow and return sides of the primary circuit, and each has its own heat exchanger and control valves.

Suppliers of heat, from energy which would otherwise be wasted, can be selected so that the primary circuit is maintained at the desired temperature. Each consumer is separately supplied with the flow it needs to provide the required amount of heat.  A PLC-based control system allows the operator to oversee the status of the plant on-screen, select suppliers and consumers and set the  consumer temperatures. Once this has been done, the control valves work automatically to give the results required by the operator.

The company had previously used waste heat to heat and cool accommodation, produce fresh water, provide sanitary hot water and to heat tanks. Using those solutions, the company claimed that around 60% of waste energy generated onboard could be used. This year it has added to that basic system with solutions for de-icing, ballast water treatment, water cooling and power generation – and it claims that 75% of waste heat can now be put to use.

The Climeon power generation system uses waste heat from three sources – exhaust gas, high-temperature water and low-temperature water – to give a product range of 150-600kW. Given that it can take 2,000 litres of fuel to generate 1kW of pump efficiency, the potential saving is clear.

The company has secured a patent for a new de-icing system. By circulating hot water in an inner tube inside the railings, hot water is transported 20m in each direction before returning to the centre of the system – maintaining the same temperature across a 40m range. This avoids the common de-icing issue of water temperature dropping as it travels around the system.

The company can also use waste heat to power a ballast water system that is currently under tests prior to submission for IMO and US Coast Guard approvals. The system pasteurises and filters water, with the required heat maintained by circulation – with the already heated water given a temperature boost and then being circulated to provide heat for water coming into the system. A slow-flow system ensures that the water circulates at the rate required to ensure its temperature is maintained.

The Pyro waste energy cooling system also leads to pumping energy efficiencies, using frequency controlled pumps to reduce the flow needed to cool water. This allows vessels to reduce the number of pumps on board; for a recent installation on a 140m offshore construction vessel, Ulmatec Pyro was able to more than halve the number of cooling pumps and seawater heat exchangers, just adding four freshwater heat exchangers.

“If the vessel needs 15.000kW of cooling effect during a year, you can save as much as 100kW in reduced pump effect with our system, which equals around 200,000 litres of fuel a year,” says Urke. “This is made possible by using fewer pumps, and by the control of automatic regulated valves, which pumps strictly the required volume and flow of cooling water.”

The motivation for operators to install such systems is clear. As Urke explains: “Marine gas oil price is going up and down. Currently the cost is about US$500 per tonne, and has been up to US$960 per tonne, but is generally expected to increase dramatically the next te- to twenty years. This has a huge impact, both on running costs, and emissions to the environment.”

There are clearly efficiencies to be gained, although the low numbers of vessels fitted with such system attests to potential obstacles in cost and complexity. As the need for efficiency becomes more pressing, ship operators will continue to look even more closely at developments in the sector.

Sourced by ekomeri.com

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