Commercial Scale Long-Term Mussel Live Holding Facility

Final Report
Allen’s Fisheries Ltd.
AIMAP-2010-N06

Table of contents

1. INTRODUCTION
2. INSTALLATION
3. COMMISSIONING
4. OPERATION

1. INTRODUCTION

In 2004 Allen's Fisheries Limited (AFL), with assistance from the Centre for Aquaculture and Seafood Development (CASD), constructed a live holding system for mussels. The main benefit of this system was that it allowed the company to hold product prior to processing. This ensured that the company could supply market requirements for a full 12 months. Other benefits of this system included regaining yield lost as a result of drainage during harvesting and shipping, improved capability to handle variations in market demands, and reduction in labour costs.

In 2010, Allen's Fisheries with the support of DFO-AIMAP, NRC-IRAP and the Canadian Centre for Fisheries Innovation (CCFI) requested the assistance of the CASD in designing and testing a commercial scale large capacity live holding system. Allen's Fisheries identified existing buildings that were underutilized in recent years and the intention was to convert one of the buildings, convert all of the underutilized buildings or to build an extension onto the existing live holding building to enable a new live holding system. The buildings had ample space and some equipment and infrastructure that could be utilized for long term holding of mussels.

A full assessment of the AFL infrastructure was completed by December 2010 and a conceptual design was prepared.  Marine Institute (MI) personnel provided the full suite of models, drawings and agreed to specifications to AFL. AFL has commenced with purchasing of the equipment and sourcing contractors to construct the pump house and plumbing requirements for the holding system. The total cost of the hardware purchased by AFL is approximately $440,000.

It was not possible to install and test the system for the 2011 season due to the long lead times on some components and unexpected delays for the delivery of the filtration equipment. Allen's Fisheries now have the hardware on hand and are planning the installation of the equipment for November and December 2011 to be ready for live holding of mussels in early 2012.  AFL has requested support  from the Centre for Aquaculture and Seafood development during the install and commissioning of the system to ensure that everything is installed  as per the conceptual design and that the system  functions as intended.

The following report outlines the work CASD performed in support of the live holding system installation and commissioning.

2. INSTALLATION

Support during the installation was provided through conference calls, review of progress reports and photos, and evaluation of changes to the proposed system.  There are a number of differences between the proposed layout and the actual installed configuration including repositioning of components, changes in pipe sizes, and omission of components that did not arrive in time. These differences are outlined in the following sections.

A site visit was planned during the initial installation stage.  Based on the speed of progress with the installation, it was decided between the CASD engineer and Allen's Fisheries that a site visit was not necessary.

Component Layout
The physical layout of components in the pump house is different than shown in the original concept drawings.  Equipment was repositioned to make space for a separate room to house the electrical panels and variable frequency drives (VFDs).  The equipment in the pump house is closer together but no problems are anticipated as a result of the change in layout.

Suction Line
The underwater suction line that was installed is a smaller diameter and extends further out than allowed for in the conceptual design.  The original calculations we done based on a 12" suction line 40ft out. The actual length of the suction line is approximately 1000 ft.

Only 8" pipe was available within the timeframe available for the installation. The flow calculations were repeated to determine if an 8" pipe at 1000 ft length would be sufficient for a single pump.  It was determined that the net positive suction head available (NPSHa) was insufficient when the filter was in backwash mode.  Approximately 9.36 ft of suction head was required but only 6.5 ft was available.  In filtration mode the NPSHa was sufficient with 12.8 ft available and only 5.6 ft required.

The calculation was repeated using two parallel 8" pipes for the suction line.  This setup can supply one system with the filter in either filtration or backwash mode.  Allen's Fisheries decided to install two 8" suction lines for this season and limit the number of live holding tanks to 120 which is the recommended maximum number for one system supplying 500 gpm of flow.  The remaining two systems will serve as backups in case of problems.

Discharge Line to Live Holding
The discharge line from the pump house to the live holding area was to be 10" diameter. A 6" diameter line was installed instead which means less flow to the holding area and therefore fewer tanks that can be used.

As a guideline, a safe maximum velocity of water in PVC piping is 5 ft/sec.  This is to avoid issues with water hammer. The velocity in the 6" pipe with 500gpm flow from a single filter system will be 5.6 ft/sec. While slightly over the recommended maximum, it is close enough that no problems would be expected with pump operating. The 6" pipe is sufficient when operating one pump and filter system to supply 120 live holding tanks.

Recirculation from Discharge Header to Suction Header
The recirculation line from discharge header to suction header is not installed yet. Excess filtered water must be discarded to the drain instead of being recycled back to the pump suction. This arrangement is less efficient in that it filters more water than it needs to.

The recirculation line is also a safety measure to prevent over-pressure in the discharge header. If valves are closed in the live holding area the pump will be supplying mo re water than is required and discharge header pressure will begin to rise. The control valve in the recirculation line will open to divert the excess back to the pump suction.

At the time of this report the control valve had not yet arrived.  It will be installed as soon as it’s received.

3. COMMISSIONING

The CASD engineer, two ARKAL filter technicians, and a technician from Electric Pump and Motor travelled to Allen's Fisheries in February 2012 for the initial start up of the system.

Gasket Leak in UV Unit
On first start up there was a large leak in the seal around one of the UV units. An inspection of the end plate revealed that the lower 2 bolts were loose.  These bolts had to be removed to install mounting brackets and they we not properly tightened when replaced.  The end plate was removed, the gasket was cleaned and re-seated, and then the end plate reinstalled.  All bolts on the end caps were checked and tightened on all 3 UV units.

Pump Priming
Priming the pumps proved difficult.  There were many leaks in the header causing a loss of vacuum on the suction side of the pump.  The header was drained, welds repaired and the header pressure tested. The water supply to the priming line for the suction header was not connected during start up.  The pumps had to be primed by flowing water back through the whole system from within the live holding area.  It took several attempts to establish and maintain a proper prime on the pumps.

Cold weather has made it impossible to properly glue the PVC pipe and complete the installation of the priming line. This work will be done when weather permits.

Backwash Drain Lines
The drain lines from the filters were tied together into a common 4" diameter drain pipe running under the floor.  This drain was connected to the drain holes in the floor.  During backwash there was enough flow to cause water to back up in the drain line and spill onto the floor through the other drain holes.  A temporary 4" flex line was installed to bypass the in-floor drain and pipe the backwash water directly to the outside. Permanent 6" drain lines will be installed for each filter to handle the backwash water.

Cold weather and snow build-up had made it impossible to complete the installation of the drain lines. This work will be done when weather permits.  The temporary flex line will continue to be used in the interim.

Air Purging
Air relief vents were to be installed at all high points in the piping system to allow trapped air to escape. Not all of the air relief vents arrived in time.  A high point in the piping between the UV units and the discharge header had no vent and it seemed that air was being trapped there.  All air must be purged from the piping for the system to operate at its best.

There have been continued delays in the arrival of the air vents. They will be installed as soon as they are received.

Filter Programming
The differential pressure (DP) sensors did not arrive with the filters. The DP sensors trigger a backwash cycle when the pressure drop across the filter exceeds a preset limit.  In the interim, backwashing was set to occur at timed intervals until the DP sensors arrive.

The supplier recommends setting the filters to backwash at regular timed intervals. Records of backwash times and trigger events are logged in the filter controller.  Daily reviews of the backwash logs should be done to check for backwashes triggered by DP.  If DP is triggering too many then the interval between timed backwashes needs to be reduced.   DP triggered backwashes are a backup to timed backwashes and can be used as a tool to gauge changes in water quality over time.

The DP sensors have since been installed and tested.  The filters remain set to backwash at timed intervals with DP triggered backwashes as a backup.

4. OPERATION

At the time this report was prepared there were no mussels in live holding.  Ice in the bay is later than expected so there has been limited need for live holding.   The existing capacity in the original live holding area has been sufficient to date.

All three systems are operational and ready to use.  Each one has been adjusted and run overnight to ensure uninterrupted operation.