A Paper on 40 μm Ballast Filter Operating Experience on a Crude Oil Tanker

Background:

The Ballast Water Filter system equipped with 40 μm mesh size was tested aboard the Crude Oil Tanker. The achievable flow rate for this filter is between 500-1,000m3/hr. The primary objective of the filter testing was to find out whether a selected filter technology installed on board of Crude Oil Tanker (transporting oil, regularly between Valdez, Alaska and other major ports in western USA) would be able to operate in challenging water conditions at various times of the year. The main concern of the customer was a varying TSS concentration in ports located in San Francisco Bay.

A joint test plan was developed between the Ballast Water Treatment System (BWTS) maker and the Filter company with the intent that following items could be determined, so this will help the customer to make a decision on selected filter technology that will be used in conjunction with Slip-stream Electrochlorination-based BWTS:

1.    Determine uninterrupted filter operation in varying water conditions along west coast of the United States.

2.    Determine overall sediment (particle) removal rates (Measured in NTU levels).

3.    Determine operating flow rates of filter unit over time and at varying water conditions.

4.    Determine the ability to recover from “over load” conditions to normal filter operation.

In addition to 40 μm filter, following equipment and/or instruments were used in the test:

1.    Filter Backpressure Control Valve to provide sufficient backpressure to the outlet side of the filter to facilitate and efficient back flushing process.

2.    Differential Pressure Flow Transmitter was used to measure in-line filter outlet flow rates.

3.    Pressure Transmitter was used to measure inlet and outlet pressures through the filter.

4.    In-line TSS sensor was used to measure inlet and outlet turbidity values through the filter.

5.    Data logger was used to record flow rates, pressures, and turbidity values at every 10 seconds.

Table 1. Summary of Operating Parameters for Various Filter Operations (Tests) along West Coast of the United States

Test observations:

1.    The 40 μm filter provided flow throughput greater than 85% of design flow, when operated in water conditions with low turbidity (ports/ docks with clean water) varying from 5 to 45 NTU. But, when turbidity levels increased above 100 NTU, the design flow throughput decreased well below 40 to 50% of design capacity. At these times, backflush was more frequent than normal operation.

2.    As the turbidity levels approached 250 NTU (see fig. 5), the filter was constantly in backflushing mode and when turbidity levels approached 300 NTU (see fig. 5), operator reduced the filter inlet flow rate to keep the filter from clogging or damaging.

At times, filter inlet turbidity levels exceeded 400 NTU for a very short time during a low tide and minimum underwater clearance of 2.0 meter. During filter operation in turbid water, it was necessary to use Manual Flush Mode to keep the filter running. Operator acknowledged that it was challenging at times to keep a balance of maximum flow rate without clogging or damaging the filter. The filter operation required continuous oversight for running it optimally without it being damaged (ref: chief engineer of the crude oil tanker). The filter recovered from “over load” condition because of manual intervention by an operator. It is evident from test data that the 40 μm filter will provide a significantly reduced filtered flow without being clogged, only if the operation is being constantly monitored by n operator in “over load (high turbid water)” conditions.

Figure 1. 40 μm Filter Operation on board Crude Oil Tanker in Long Beach, California

Figure 2. 40 μm Filter Operation on board Crude Oil Tanker at Chevron Dock located at Richmond Long Wharf Terminal in Richmond, California

Figure 3. 40 μm Filter Operation on board Crude Oil Tanker at Valero Benicia Refinery Dock in Benicia, California

Figure 4. 40 μm Filter Operation on board Crude Oil Tanker at Chevron Dock located at Richmond Long Wharf Terminal in Richmond, California

Figure 5. 40 μm Filter Operation on board Crude Oil Tanker at Valero Benicia Refinery Dock in Benicia, California

Figure 6. 40 μm Filter Operation on board Crude Oil Tanker at Shell Martinez Refinery Dock located in Martinez, California