Maritime Emission Manager Course

This refers to pumps, fans, compressors, etc. that are extensively used on-board ships. There are a number of opportunities to save energy and reduce potential emissions with these machineries that are briefly discussed. The main areas of evaluation include:

Sizing:

 The sizing of machinery against the actual operation requirements needs to be checked in order to identify cases of over sizing. This can be carried out by monitoring of the machinery operational performance against manufacturer’s specification. In addition, the following may be indicative of oversized machinery:

• Continuous throttling of flow in order to match supply with demand (e.g. permanently fixed valve or damper positions).
• Short periods of operation when the machinery is used in on-off mode. For example, in a compressed air system, an oversize compressor will supply air to tank in a shorter period of time than a rightly sized compressor.

For each machinery, a “capacity factor” can be defined that is indicative of over-sizing or under-sizing. Capacity factor may be defined as the “operational capacity” divided by “design nominal capacity”. A capacity factor significantly below or above unity is indicative of poor sizing or system’s operational anomalies.

Operation profile: The operation profile of machinery represents the machinery’s load versus time. Continuously operated machinery at a certain load will represent a steady operation profile.

Machinery with highly variable load will represent a non-steady load profile. Load and operation profiles are normally presented in histogram format, an example of which is shown in figure below.

Figure 23: Load profile for a typical pump (MariEMS 2017).

From operation profile, operation management strategy of the machinery could be decided. In particular, method of control and choice of on-off or Variable Speed Drive (VSD) modes can be established. For variation of flow, two methods of flow control could be used (see figure below):

• Valve system modulation (changes to valve open area) is the traditional way of flow control. This method of control is energy inefficient.

Figure 24: Main types of flow control (MariEMS 2017).

 Variable Speed Drive (VSD) is used to control flow without throttling. This is the most efficient way of flow control for fluid rotating machinery (see figure 25 below).

Figure 25: Impact of Variable Speed Drive method of flow control on power demand (MariEMS 2017).

The load profile for a multi-machinery setup could provide valuable information on method of load sharing strategy and management between machinery.

Operational aspects

Based on the above evaluation and basic characteristics of fluid machinery, the main opportunities for energy saving are and emission reduction are:

Fouling reduction: Fouling in fluid machinery is a common cause of performance deterioration. Fouling can be controlled via best-practice maintenance activities. For examples, fans are very sensitive to inlet fouling.

Multi-machinery management: In general a multi-machinery configuration (e.g. chiller plant compressors), the minimum number of machinery running for a particular duty represents the best machinery management strategy and ensures minimum overall machinery energy consumption.

Reducing idling mode of operation: In addition to operation of the machinery at optimal efficiency, it is prudent to reduce the none-productive operating hours of all machinery especially during port stays and also change over from on to off modes and vice a versa. In general, the following policies should be implemented:

• Each machinery should be operated at its optimum efficiency.
• The none-productive hours of operation must be minimised by on-off controls. In particular, late turn-off and early turn-on of machinery should be avoided.
• Flow control and management: As discussed earlier, control of flow is an area where significant savings may be made:
• Throttle flow control: A pump with variable flow requirements that is controlled by throttling could save energy by:
• Replace the constant speed drive to variable speed drive (level of saving depends on the pump duty cycle).
• Replace throttle control with on-off control, if feasible (switch on and off according to demand), especially if some storage capacity can be added to the system.
• Excessive flow: For example, pump flow rates in excess of system requirements, lead to increased energy losses. To avoid:
• Ensure that pump flow is controlled according to process requirements.
• Review and adjust control settings.
• Demand control and demand reduction: The need for flow should be investigated at the demand side. Every effort should be made to reduce demand by:
• Preventing all leakages.
• Conservation policies in compressed air, water, conditioned air, etc. lead to reduced energy consumption by corresponding systems (MariEMS 2017).