The benefits of battery hybrid powered port equipment

13 Sep 2017
The use of battery hybrid technology for RTGs lessens the environmental impact of crane operations

The use of battery hybrid technology for RTGs lessens the environmental impact of crane operations

Port operators around the world are concerned with climate change for good reason because severe weather patterns will be detrimental to operations, writes Sean Puchalski, VP Strategic Marketing & Accounts, Corvus Energy.

As part of their ongoing environmental assessments and strategic planning, port operators are including environmentally sustainable technology into their operations.

Equipment efficiency

Approximately 20%of diesel fuel emissions from cargo handling equipment at ports are emitted by RTG cranes and other container handling equipment, such as automated guided vehicles (AGVs).

Container terminals use RTGs to manage container aisles, stacking and moving cargo-containers and acting as the intermediary equipment between the shore-side cranes and the truck and rail connections.

The vast majority of these RTGs utilise a constant-speed diesel generator to supply power to the crane for hoist operation, propulsion and house loads (For example, instruments, lights, air conditioning).  The disadvantage of constant-speed generator technology is that the generator runs at a constant speed regardless of the work being performed.  Therefore, during periods when the crane is idle or performing an activity that requires little power, a significant amount of diesel fuel is wasted and a significant quantity of greenhouse gas (GHG) and particulate matter (PM) emissions are produced.

All RTG crane drives are powered by electric motors using the electricity generated onboard. RTGs function by making three basic movements:

1) Hoisting (and lowering) – to raise (or lower) the spreader

2) Trolley movement – to move the spreader transversely across the stack

3) Gantry movement – to move the entire crane along the length of the stack.

The RTGs at the terminals have also been found to be inefficient in their operation and energy management due to different operational factors including:

  • Operators not allowing the RTG to power down to standby when idle for more than one hour
  • The generators running when the machine is not performing lifting operations (even when in standby)
  • The regenerated power from lifting operations being dissipated as heat through resistor banks.

When a container is lowered, the hoisting motor is not performing any work. In fact, the lowering motion is being driven by the weight of the container, therefore the movement has the potential to produce electricity (analogous to a generator). In a conventional RTG, no way exists to gainfully use this generated electricity. Therefore, the electricity is fed to large resistor banks, converted to heat and eventually dissipated via direct contact with air.

Power regeneration mode can be up to six minutes per hour for RTG cranes. Additionally, the need for maximum power on an RTG’s diesel engine exists for only 4% of operating time, which means that the peak power demand can be reduced and the diesel engine can be downsized.

One way to capture the energy generated in an RTG crane’s lowering motion is by storing the energy in onboard battery banks. This stored power can then be used to:

1) Reduce the peak load demand on the engine during the next hoisting operation

2) Supplement the electric power supplied by the diesel generator

3) Run auxiliaries like computers, lights and air conditioning, allowing the engine to be shut down during idle periods.

Battery technology

The use of battery hybrid technology for RTGs lessens the environmental impact of crane operations by reducing fuel consumption and harmful fossil fuel emissions.

Installations like this are happening in China, SE Asia, Europe and to some degree the USA. In countries where the electricity grid is well developed and robust, ports are opting for all-electric RTGs tied right into the grid.

However, in a large part of the world where the grid infrastructure cannot handle the load requirements, port operators are looking to hybrid power solutions which combine batteries with diesel power systems.

The punishing part of the load profile on the battery is the large inbound power spike when the container is lowered.  This results in a rapid charge event on the battery.  Normally this energy is wasted through large resistor banks (to heat), but in the Corvus case it is recycled for useful work on the next lift. This operation requires a high-quality battery as typical batteries will degrade rapidly under these conditions. Also, this battery technology allows the significant genset size reduction that enables great fuel savings.

Retrofitting existing RTGs and AGVs replaces the conventional diesel power plant (typically rated between 400 and 750 kW) with a much smaller diesel generator set of 50 - 150 kW when combined with a battery-based energy storage unit.

Environmental considerations

Besides cost considerations, ports must consider how air quality, both locally around the port and globally, is impacted by their operations. The communities near ports are often sensitive neighbours with whom the ports need to maintain healthy relations.

RTGs are the leading contributors to diesel emissions at the terminals besides the ships berthed during container loading operations. The following section summarises the relative impact of a hybrid electric RTG retrofit on CO2 emissions, as well as emissions of NOx, SOx, and PM10 (particulate matter less than ten micrometres in diameter). Percentage reductions of the various emissions are benchmarked from the standard of an engine meeting Tier 1 emissions standards. (The Greening of Rubber-Tired Gantry Cranes in Ports, 15.915)

  • CO2 Emissions – 60% reduction
  • NOx Emissions – 90% reduction
  • SOx Emissions – SOx emissions are a function of sulphur content in the fuel used and quantity of fuel consumed.
  • PM10 Emissions – 90% reduction.

Hybrid cranes

How hybrid cranes save fuel:

  • Regenerative braking energy is captured and stored as electricity when a container is lowered. This recaptured energy is directed to the Corvus ESS, reducing the amount of power required from the generator
  • In the conventional RTG configuration, the diesel generator undergoes periods of inefficient sustained idling, resulting in unnecessary fuel usage. With the Corvus ESS in place the diesel generator is shut down during traditional idling times, allowing the RTG to operate on “full electric” battery power. Cranes equipped in this manner are proven in the field to operate at optimal efficiency. Unlike conventional diesel electric port cranes, a hybrid version is powered primarily from the ESS resulting in fuel savings of up to 65% with the added benefits of reduced operating costs with less greenhouse gas emissions and lower noise levels at the terminal.

The hybrid RTG crane market is set for growth as operators seek to drive down their fuel costs while reducing emissions. There are thousands of existing RTG cranes in global ports that could potentially be retrofitted with hybrid power systems, while hundreds of new cranes are built every year for the global market. The impact of converting even some of these RTGs to hybrid power is extremely significant.

According to accepted standard emission calculations, an energy efficiency programme that reduces greenhouse gas emissions by 4,700 metric tonnes of CO2 per year has the same impact as removing 1,000 vehicles from the road. The 26 RTGs operating with Corvus ESS technology will eliminate 5,300 metric tonnes of CO2 per year equal to removing 1,143 cars from the road. Given the thousands of RTG cranes and other pieces of port equipment around the world, the potential environmental benefit of implementing hybrid power is enormous.

Battery solution

For the past five years, Corvus Energy has been supplying an increasing number of ports with hybrid power solutions. With dozens of RTGs now being powered by a Corvus ESS, Corvus Energy has designed and built the optimal battery solution for port equipment. The next generation ESS from Corvus Energy is called Orca Energy ESS.

Earlier this year, Corvus announced that it will provide Orca Energy lithium-ion energy storage systems for four hybrid RTGs for CCCC Shanghai Equipment Engineering (CCCCSEE). The RTGs are the first of many cranes at the Chinese Port of Changshu to undergo a diesel to battery hybrid conversion using a Corvus Orca ESS. This order represented the first port equipment order to leverage the industry leading performance, safety, reliability and cost effectiveness of the Orca Energy ESS which provides more power while taking up less space at a lower weight.

The latest order from CCCCSEE for the Port of Changshu, once again proves the viability of energy storage for the hybridisation of industrial equipment such as port cranes. The design and performance of Orca Energy enables the ESS to support aggressive load profiles with a significant reduction in cost.

With dozens of RTGs now using a Corvus Energy ESS, Corvus technology continues to be ananswer for progressive port operators worldwide, who seek to increase efficiencies while reducing emissions and the environmental impact of their operations.

Gao Jianzhong, chief engineer, CCCCSEE, said:  “Corvus has positively shifted the economics and viability of converting diesel port equipment to battery hybrid-electric with Orca Energy. Exceeding all requirements and expectations with Orca Energy ESS, Corvus technology is a solid cornerstone of our advanced technology solutions strategy and the proven performance, durability and reliability of its battery systems is ideally suited to the demands of our industrial applications.”

Market expansion

The implementation of a hybrid electric system provides significant fuel savings and greatly reduces GHG emissions. Unlike conventional diesel electric port cranes, the hybrid version is powered primarily from the Energy Storage System (ESS) resulting in fuel savings of up to 65% with the added benefits of reduced operating costs, reduced greenhouse gas emissions and lower noise levels at the terminal.

The ESS provides the required power for lifting and hoisting activities, as well as moving the cranes between rows. The ESS is installed to supplement the generator and the generator is required to charge the ESS during operations. The RTG’s primary generator can be replaced with a smaller generator unit. The smaller generator operates much more efficiently running constantly close to its most efficient power level. The ESS also provides a mechanism to capture regenerated power from the RTG’s lifting activities. Regenerative power is captured in the ESS during lowering of containers on to trucks or the stacks and this regenerated power can be used to charge the ESS.

In the near-term, two things are happening in the port industry, firstly, the impetus to move towards green tech and sustainable operations has now passed the tipping point. Secondly, energy storage technology such as the Orca ESS from Corvus has proven to be reliable, safe and cost effective.

Together these conditions are creating a massive opportunity for companies like Corvus Energy as more and more port operators are switching to all-electric and hybrid port equipment. This movement is happening to a greater degree in Asian ports where port expansion and container traffic growth is accelerating and grid infrastructure prohibits fully-electric port equipment. Corvus Energy is well positioned to expand into these markets with its global technology partners.

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