Fishermen's News - The Advocate for the Commercial Fisherman

The New Neah Bay Ice Plant: An Educational Tour

 

The new ice plant at Washington's Neah Bay makes around 4,000 pounds of ice an hour, can store up to 110 tons of ice, and can deliver it to fishing boats via two icing stations at a rate of 30 tons of ice per hour. Photo courtesy of Robert Buckingham, Port of Neah Bay.

2014 was a busy year in the fishing industry: new high tech fisher-processor vessels, new equipment in existing boats and land-based facilities and a lot of consolidation within the industry – all good news that the industry has confidence in the future. Out on the westernmost point of the lower 48, the Makah reservation Port of Neah Bay began construction of a new high tech dock and ice plant. The goal was to produce an environmentally responsible capital investment of substantial durability that would serve the industry and future generations of Makah in their fishing birthright. After months of planning and design, the construction began with the demolition of the old port dock, environmental cleanup, and the construction of a new concrete dock with the latest technology in seismic and environmental design. The project included an all purpose dock building, plus a state-of-the-art ice plant supporting 52 tons per day ice making capacity, a 110-ton ice storage capacity, and two icing stations, each capable of metering and delivering 30 tons of high quality flake ice per hour.

Imperial Brown Manufacturing Co. provided the icehouse structure. Imperial partners with North Star Ice Company to produce high quality prefabricated insulated panel structures for ice plants that includes the penthouse that houses the ice machine. The structural support for the North Star ice machine, which weighs in at close to 10,000 pounds, is included in the Imperial package. Between North Star Ice and Imperial Brown Manufacturing, the entire ice plant is delivered and ready for assembly, down to most of the hardware and appurtenances. Highland Refrigeration provided the refrigeration equipment and installation with the piping executed in Stainless Steel. Highland also provided the construction and assembly of the Imperial structure and North Star equipment in a subcontract partnership with Roy Pitman Enterprises. This project was constructed under Manson Construction Company in their larger public works project to replace the old dock.

I would like to take you on a tour of the ice plant and include a discussion on refrigeration. By the end of our little tour, you will have some very basic understanding on what refrigeration is and how it works.

The icehouse is around 53 feet by 48 feet and located on the northeast corner of the dock. On the roof of the icehouse is some of the refrigeration equipment and a penthouse for the North Star model 90 ice machine. Please follow me as we climb the long stairway at the end of the dock to the penthouse entry door on top of the icehouse.

As we step inside the penthouse, we see that the interior space is dominated by the North Star ice machine. It is a large vertical cylinder around 5 feet in diameter and 10 feet high, insulated and finished in a white and blue fiberglass shell. We climb a short ladder to the inspection platform so that we can look down into the ice machine through the Plexiglas inspection hatch cover. What we see is quite amazing: there is a large mechanical rotor assembly that slowly rotates inside of this cylindrical ice drum. The purpose of this rotor assembly is to distribute a continuous flow of water across the interior freezing surface of the drum and harvest the resulting ice. It is really fascinating to watch as the water freezes and becomes thicker as it adheres to the ice drum before being peeled off in flakes about an inch in width. The cascade of ice flakes fall into the ice bin below.

What causes the water that cascades down the freezing surface inside of this ice machine to freeze into ice? Well, on the other side of the freezing surface is liquid ammonia refrigerant. The refrigerant is absorbing heat from the water by boiling – changing from a liquid to a vapor. It removes so much heat that the water can no longer support a liquid state, so it freezes into ice. This is curious: what does boiling have to do with absorbing heat? To illustrate the answer, consider a pot of water on the electric burner of your stovetop at home. Remove the pot of water, and the electric burner glows red hot. Put the pot back on, and it loses that red glow as it cools down – well, it's still hot, but not red hot. The boiling of the water is refrigerating the electric coil down to a lower temperature. The boiling point of water is 212°F. The water will continue to absorb heat and refrigerate the burner coil until all of the water has boiled away, but while it is boiling, the temperature will not change, even though it is absorbing a tremendous amount of heat. The water vapor that is produced by boiling contains all of the energy that it absorbed from the burner coil in a hidden form of energy that we call "latent heat".

Boiling water is an excellent example to use in describing how refrigeration works: however, ammonia and water are different compounds, and as you would expect, they have different physical properties. At atmospheric pressure, water boils at 212°F. At this same pressure ammonia refrigerant boils at MINUS 28°F. Are you getting a hint on how refrigeration works?

What happens to the ammonia vapor that is produced through the boiling liquid ammonia? The vapor pushes out of the ice machine into the large "suction pipe" that is connected between the ice machine and the compressor that is located in the mechanical room in the dock building. Now let's go downstairs and take a tour of this compressor.

Down in the compressor room, we see a large machine, taller than a man, and about twice as long. This is the ammonia compressor unit and it includes a two hundred horsepower electric motor. What do we get for the energy packed into this 200 horsepower motor? All of this equipment has been purchased and installed for the purpose of making 52 tons of ice every 24 hours. That is more than 4,000 pounds of ice per hour, all of it for the purpose of delivering quality seafood to the Port of Neah Bay dock; seafood that will find its way to the dinner plates of their metropolitan neighbors to the east.

The compressor receives the entire volume of vapor that evolves from the boiling ammonia as the machine turns water into ice. We call it a "compressor" because it compresses this low-pressure ammonia vapor into high-pressure vapor that is then pushed up to the condenser on the roof of the icehouse. At this higher pressure, around 150 psi, the ammonia is at a condition where it is ready to give up its heat – the same heat that it absorbed in order to turn water into ice. As the condenser takes the heat away, the high-pressure vapor cannot maintain it's vapor state, and it condenses back to liquid ammonia. This liquid ammonia travels back to a storage tank – a "high pressure receiver" - where it can be used to replenish the ice machine.

The condenser is a simple yet very interesting piece of equipment. It is used to push the heat that was absorbed in the making of ice into something that can easily absorb it. In most cases it is outdoor air or seawater, since there is plenty of air and seawater around to absorb heat. Before we go any further, we need to understand a little physics: Both the boiling temperature and the condensing temperature of substances are dependent on the pressure exerted on that substance. So you can get ammonia to boil and absorb heat at -28°F, if you hold the pressure at close to atmospheric pressure by adjusting your compressor capacity. You can get the vapor that results from boiling to give off its heat at 85°F if you raise the vapor pressure to 150 psi with the compressor. And if your outdoor air temperature is 75°F, the heat that the vapor gives off in condensing at 85°F will easily flow across the condensing tubes into the air!

So to complete the circle: If we maintain the pressure imposed on liquid ammonia at close to atmospheric pressure (zero psi), the boiling point of that liquid will be -28°F, and any heat coming across the freezing surface as we make ice will cause the -28°F liquid to boil into -28°F vapor, storing all of the heat in the vapor state as "latent" heat, without any change in refrigerant temperature. Now, let us pull that vapor into a compressor and pump it up to 150 psi where the condensing point is at 85°F (although the actual vapor temperature will be much warmer than 85°F due to other factors). If we blow 75°F air across the condenser tubes, the hot vapor temperature will drop to 85°F vapor, condense into 85°F liquid and convert its latent heat back into sensible heat by handing the energy off to the cooler air that passes through the condenser. The 75°F air that enters the condenser, will leave at a substantially higher temperature since it now contains all of the heat that was absorbed in the process of turning water into ice. This is the summary of the complete refrigeration cycle. It is worth pondering and struggling to understand if you intend on including refrigeration as one of your skills in life.

The Neah Bay condenser has an added feature in that it uses water and powerful fans to gain additional cooling through evaporation of the water, and thus have a more effective condenser that operates at a lower condensing temperature than is possible with a dry air condenser.

Down below the ice machine is the icehouse. The icehouse is a cold storage building containing a large ice bin, an ice rake, and a number of ice conveyors for delivering ice. Lets get out of this noisy compressor room and go into the icehouse. Now, button up – it's a chilly 18°F in there!

Entering the icehouse, we see that the space is dominated by the ice bin, except for narrow hallways on the north and east sides. The ice bin is around 45 feet long, 13 feet wide and 10 feet high. Since the ice machine makes around 4,000 pounds of ice an hour, it doesn't take long to create a little mountain of ice in the ice bin. The ice bin is designed to hold 110 tons of ice when it is full, but in order to take advantage of the storage capacity of this ice bin we need to have a way to knock down the mountain of ice that develops under the ice machine and distribute it evenly across the whole surface of the ice bin. This is the job for the "ice rake". If you climb onto the inspection platform in the icehouse and look down into the ice bin, you will see the ice rake. It is a series of rectangular steel tubes 2 inches by 6 inches in size and as wide as the ice bin. Drive chains on the ends support these rake elements. The rake can drive in both directions to level out the ice. Each time the rake cycles through another leveling operation, the rake hoist raises the assembly up a bit in order to make room for the next ice leveling operation.

Now that we have learned something about making and storing ice, lets watch as the ice plant operator delivers ice. We are going to "ice a fishing boat." This is the whole reason for all of the expense and effort in building this ice plant, and this is what will call the fishing fleet back to the rich and fertile fishing grounds that have been traditionally referred to as the mouth of the Salish Sea; the Strait of Juan de Fuca.

The Neah Bay ice plant has two icing stations, one on the north face of the dock and one on the east face. Each is capable of delivering 30 tons of ice per hour. Today we have a local fishing boat that is tied up on the north face of the dock. He has requested 5,000 pounds of ice, and has lifted the hatch cover away in preparation for receiving ice. The north dock icing station consists of an 18-foot long elevating conveyor that starts below the icehouse floor and angles upward where it terminates ten feet overhead with an ice delivery hose connection. The ice hose is ten inches in diameter, somewhat flexible, and is in two sections. The short section, which is connected to the elevating conveyor, drops down to about chest height on the ice plant operator. He uses this hose to fill ice totes that are used in the processing facility for icing fish for the fresh market. But today we will attach an extension hose that will bring ice over the bull rail and down into the hold of the fishing boat.

The control panel, located on the elevating conveyor, has a digital readout; it is designed so that the operator can enter an amount of ice, hit the start button and from that point everything will be automatic! The ice plant operator has entered the order for 5,000 pounds of ice, attached the long hose, and lowered the other end to the deck of the boat. The crewman down in the hold will attend to the hose and direct the flow of ice to certain places in the hold so that he can store ice and use it to cover his catch as it comes in. Everything is ready, and after receiving an OK from the crewman below he hits the "start" button. The ice delivery conveyors stage on and inside the icehouse the ice rake and all of the delivery machinery go into action. A screw conveyor and ice hopper meter ice into the elevating conveyor at the rate of around 1,000 pounds per minute, so that the delivery of 5,000 pounds of ice takes around five minutes. Toward the end of the delivery, the ice rake shuts down and each conveyor and hopper in turn clears itself of ice before shutting down. The controls are calibrated so that when all conveyors and hoppers are cleared of ice and the last flake of ice falls out of the end of the delivery hose, the boat will have received its order of 5,000 pounds of flake ice.

The North Star controls are very sophisticated and extremely reliable. They have evolved over the years as delivery methods and available computer technology have changed. Of all of the control schemes that North Star has developed over the course of 50 years, the most sophisticated, and by far the most reliable are being offered today. For remote locations like Neah Bay, an ice delivery problem is usually solved by looking at the control panel display that spells out which piece of equipment is causing the problem. If that doesn't provide a cure, the operator can make a cell phone call to the North Star Technical team. The North Star tech will sit in front of his computer in Seattle and log on to the ice plant control panel in Neah Bay through an Internet connection. They will talk through the issues, perform some additional tests, and conclude the service call quickly and cost effectively. How amazing that such sophisticated technology can be placed in a remote location like Neah Bay, with the confidence that it will work well, and if something goes wrong, there will be an expedient way of solving the problem. If you look back into history, many of the North Star Ice plants that were installed in the '60s are still in operation today! The Port of Neah Bay did very well in selecting equipment that will indeed serve future generations of Makah in the years ahead.

I hope that this tour of the new Neah Bay ice plant has helped you understand some very basic technology in fishing industry refrigeration. Quite often it is these simple explanations that help launch a new generation of young technicians off on a most rewarding and fascinating career of providing a lifeblood service – refrigeration – to the local fishing fleet.

Rick Greenquist was the Project Engineer and Project Manager in the Neah Bay Ice Plant installed by Highland Refrigeration. He has taught classes as an adjunct instructor through the Seattle Community College Marine Training Center and through the Dutch Harbor, Alaska chapter of Refrigerating Engineers and Technicians Association. His focus in the last two decades has been in mechanical design of refrigeration systems, electronic controls and energy efficiency. He can be reached through his LinkedIn account.

 
 

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