5. The unloading process

5.1. Options

5.2. Unloading operation diagram

5.3. Wet unloading

5.4. Dry unloading

In our assessment of the plants in Pisco we found that the first place in the process where effluent and therefore product was being lost was in the unloading process. We contacted fishmeal producers in most of the major countries to determine what unloading methods were being used and what might be applicable to the Peruvian industry.

The discharge of industrial fish from the vessel to the processing facility has presented many challenges to the fishing industry over many years. The methods employed must not only be economical and pollution-free, but they must get the fish to the plant in good shape as quickly as possible, since the vessel must be able to get back on the fishing grounds while fish are available. Global environmental regulations in the late 1960's and early 1970's accelerated the development of new methods for discharging fish to the factory so that the various companies could meet the new developing environmental standards. In 1977 the International Association of Fish Meal Manufacturers (IAFMM now IFOMA) organized a symposium to cover this issue. Speakers were invited to address the problem of getting the fish from the vessel to the factory. The keynote paper outlined the Norwegian requirements for an unloading system that would address strict anti-pollution requirements, restricted working hours, and high labor and energy costs. These requirements are still valid today and are listed in Figure 23.

Generally speaking, there are only two ways to get the fish from the fishing vessel to the factory for processing. The fish can be moved either wet or dry. Within these two categories, there are at least seven options for unloading fish from the vessel to the plant that are or have been used in the fishing industry. These are outlined in Figure 24.

5.1. Options

5.2. Unloading operation diagram

5.3. Wet unloading

5.4. Dry unloading

5.1.1.1 Hidrostal PUMP 2:1

The Hidrostal pump has a special centrifugal screw impeller that was developed in Peru specifically for pumping fish. It is the wet pump that is now used throughout the Peruvian fishery and in some plants in Chile. The only connections between the vessel and the shore or platform is a flexible suction pipe and water hoses so there are no problems with tidal movements. The standard pump has a capacity of 50-100 tons of fish/hour and can be varied by adjusting the fish to water ratio.

5.1.1.2 Netzsch PUMP 0.1:1

The Nemo or Netzsch pump is a Mono pump which has been used in various factories for pumping liquids and semisolid materials. The pump consists of a metallic rotor and elastic stator. It is a positive displacement pump with the quantity of material pumped proportional to the speed of the pump. The pump is variable speed and reversible so that it can be cleaned out. The maximum quantity is about 250 cubic metes/hour. For unloading fish, the pump must be moved around the hold of the vessel. This can be done with a crane. This pump is being evaluated at several plants in Peru. One of the disadvantages of the pump is its weight which makes it difficult to maneuver.

5.1.1.3 Pressure/vacuum PUMP 1:1

Recent experiments with a pressure/vacuum pump have been conducted in Chile. The project developed because fish were being discharged from the vessels at the congested port and then trucked from the port through the city to the factories. The pump is reported to be capable of moving fish approximately 1600 meters with less water and less degradation. The pipelines are of high density polyethylene thermofused together and floating on the surface. Fish were conveyed a distance of 1150 meters in the water and 450 meters on land to the plant. The capacity of the pump was 200 tons/hour. See Figure 25. The pumps are electrically powered so power cables must be run to the unloading station. The pump has been successful, unloading 35,000 tons of fish with a ratio of 1:1 to 1:3 of fish to water. Degradation of the fish is no worse than with other unloading methods. These pumps are now operating in Peru and Chile on a variety of species including anchovy.

5.1.1.4 Others

The Superfos Hydraulic transport pump was developed in Denmark in 1973. In looking for an alternative to the wet system, their requirements were:

1. Minimum destruction of raw material.
2. Transportation without the addition of water.
3. Closed system.
4. Minimum maintenance.

The pump is a double-acting piston pump with a four-way valve as the central point. The action of the pistons and the rotary motion of the valve flap allow only one motion to happen at a time. No air or water is used and the actual capacity is 60-80 cubic meters/hour.

In the USA, fishmeal plants use Humphreys piston pumps to unload the fish. These are similar to the Hidrostal pump in that water is used to convey the fish from the vessel into the factory but unlike other systems, the water is screened and recycled in the US factories and finally evaporated to become part of the finished product. By recycling the pumpwater the US plants are able to maintain a 1:3 water to fish ratio.

5.1.2 Dry

The bucket elevator (Figure 26) consists of a bucket that moves the fish to a conveyor, which elevates the fish out of the hold of the vessel and finally to a receiving bin in the factory. While it is less likely to cause pollution of the harbor and surrounding waters, it is affected by tidal changes, cannot be installed on the fishing vessel and is labor intensive. The chainpump-elevator system was used in Denmark. It acts like a pump when the fish are soft and as a bucket elevator when the fish are fresh and firm. It was replaced by the grab because of problems with large tidal changes in the North Sea and North Atlantic.

The Grab (Figure 27) consists of a clamshell or grab at the end of a crane which is attached to a dock. Its disadvantages are the spillage and drippage of fish and liquid onto the dock and into the surrounding waters. It is labor intensive and requires some other method to remove the last traces of fish from the vessel hold. Neither the Grab nor the bucket elevator are used by the fishmeal industry today. Both have been replaced by more environmentally and labor friendly methods.

5.1.2.1 Myrens pump

The Myrens dry pump offers two alternatives to mounting. The pump can be handled by a crane and lowered into the hold of the vessel (Figure 28) or mounted on the vessel (Figure 29 and Figure 30). The pump is a positive displacement pump with a rotating valve. The system operates dry, except for the water that is in the hold of the vessel with the fish. No extra transport water is used. At 45 rpm the pump will move 70-80 cubic meters per hour. Pump bearings and seals are of plastic. The Myrens Pump is currently used in Iceland with excellent results. Only a small amount of water (10%) is needed to get the pump started. Pumps of this type are also used in the factory for moving fish around the plant. The Myrens pump is no longer manufectured, but an Icelandic company has just negotiated the rights to manufacture the pump.

5.1.2.2 Iras system

A pneumatic off loading system (IRAS System) (Figure 31) that was designed to handle different species as well as different degrees of freshness and quality was developed in Denmark. The fish and air are sucked from the hold to the separation section where the fish slide down a tube which is closed by a flap valve. When the weight of the fish in the tube is large enough to overcome the vacuum, the flap opens and the fish slide out. The air escapes from the separating section to a cyclone where smaller particles of fish are collected. The air is then either discharged or recycled back to the fish again. Capacities of 1-2 tons/minute on a 200 HP plant have been achieved.

The unit is maneuverable and the hose can be moved from hatch to hatch. The noise level is also reduced. The IRAS System is used in Denmark today. Figure 32.

5.1.2.3. South African System

A dry off loading system is being used in South Africa today (Figure 33). They have unloaded an average of 50-100 tons anchovy/hour with breakage in the range of 2-3%. The fish enter the system by a suction nozzle and are conveyed through pipes to the separator. The fish are discharged from the separator through a slide box valve. According to the author, power requirements of 0.7 to 2.5 horsepower/ton of fish are needed. Figure 34 shows a slide valve instead of a rotating valve.

5.1.2.4 Containers

Some research projects were done in Chile. Fishing vessels that bring in fish for food use and also fish for fishmeal use can be handled using containers and an icing and recirculating technique developed in the UK. Containers are stacked in the central part of the fish hold and reach from the floor to the deck. The containers are separated from the rest of the hold by walls of wood or aluminum. The containers are prefilled with ice before the vessel departs for the fishing grounds, an equal amount of sea water is added and the air circulation is started before filling up with fish. The containers are then removed from the vessel by a crane.

Based on our assessment of the Pisco plants and brief visits to plants in Chimbote and Coishco the current unloading operation is seen in Figure 35. Screens may or may not be used to recover solids from the water before discharge back to the sea.

As environmental issued continue to take the newspaper headlines and as the more aggressive environmental groups put pressure on the fishing industry through consumers, the discharge of the pump water has become a very critical issue and some companies have begun to look at different methods to deal with the problem. The wet unloading process has some major disadvantages (Figure 36).

5.3.1.1 Volume of water

In our typical plant (50 tons/hour - 2000 hours per season) which uses the Hydrostil pump, approximately 200,000 tons or 52.9 million gallons of pumpwater will be produced in a season. For a larger plant, 100 tons/hour, 400,000 tons or 105.8 million gallons of pumpwater will be produced. If you multiply the single plant volume by the number of fctories in the area, the numbers can get very large. The pumpwater can contain as much as 5.7% total solids if it is not screened or 5.1% total solids if it is screened. At this time we have no data available on the semi-wet pumps to compare with the Hidrostal.

5.3.1.2 Salt content

The total solids content of the water is difficult to deal with because the Pacific Ocean water contains over 3% salt. But the salt is in the pumpwater and must be dealt with or eliminated.

5.3.1.3 Yield losses

We mentioned that for the Pisco project we decided to use the Protein + Oil content of the effluent instead of total solids or salt free solids because the protein and oil can only be coming from the fish (unless it is coming from your neighbor's effluent). If we look at the protein + oil content of the pumpwater we find that it will have an average of 2.6% if the water is not screened (51 kg/ton of fish) or 1.6% (31 kg/ton of fish) if it is screened. This means that just screening through a 1 mm screen will recover about 38.5% of the solids in the water. The 1.6% solids that is discharged in the effluent (15657 mg/l) works out according to our calculation to 34.8 kg of fish meal per ton of fish. With a value of $381/ton for the fish meal, this equates to US$13.24/ton of fish processed that is lost. Figure 37 outlines the tons of fishmeal that could be lost for each of the ports both with and without screening. Data is based on a five-year average for landings and fishmeal price.

We have defined dry unloading as the system that uses no water or just enough water to seal a valve. The grab and crane and bucket elevator system will not be discussed since they are not practical anymore except in special cases. The Icelandic Myrens pump might not be able to move the fish the distances required and would need several booster pumps along the line to keep the fish moving. Several people have mentioned that the dry and semi dry pumps cannot handle anchovy because they dry out and plug the line causing a shutdown of the unloading operation and others have mentioned that some of the semi-dry pumps are very heavy and difficult to manage. Besides these issues, dry unloading has some other disadvantages which are shown in Figure 38.

5.4.1.1. Logistics

The disadvantage of the vacuum unloading system is the limited distance that the fish can be transported. If the vessel cannot tie up adjacent to the factory (such as in many plants in South America) so that the discharge of fish is conveyed into the raw holding bins, then it would be necessary to install the unloading systems in a harbor, unload the fish at the port and deliver them to the factory by truck. This was the case with a factory in Mexico (no longer in operation) and has been tried at several locations in Chile. It is better suited to small plants because with larger plants the volume of fish would require many trucks running from the unloading area back to the factory. The other alternative is to construct piers out to the unloading stations, install the dry unloading system on the pier and run conveyors from the station into the plant.

5.4.1.2. Capital cost

Vacuum unloaders are very expensive and the cost of installation of a pier with conveyors 1500 meters out to the stations would be very expensive.