ACKNOWLEDGEMENT

The success of the 21’ A n n d Meeting of the International Institute of Ammonia Refiigeration is due to the quality of the technical papers in this volume and the labor of their authors. IIAR expresses its deep appreciation to the authors, reviewers, and editors for their contributions to the ammonia refiigeration industry.

Board of Directors, International Institute of Ammonia Refigeration

ABOUT THIS VOLUME

IIAR Technical Papers are subjected to rigorous technical peer review.

The views expressed in the papers in this volume are those of the authors, not the International Institute of Ammonia Refiigeration. They are not official positions of the Institute and are not officially endorsed.

EDITORS Christopher P. Combs, Project Coordinator

M. Kent Anderson, President

International Institute of Ammonia Refigeration 1200 Nineteenth St., N W

Suite 300 Washington, DC 20036-2422

+1-202-857-1110 (voice)

www.iiar.org +1-202-223-4579 (fax)

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Technical Paper # I 1

Compressor Hall Project

Boshra B. Shehata Anheuser Busch Companies

St. Louis, MO

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Introduction

This paper describes a new ammonia refrigeration plant, referred to as “Compressor Hall,” that replaced an old ammonia refrigeration plant. The ammonia refrigeration system in the Compressor Hall supports the operations of the oldest and largest brewery owned by Anheuser Busch Companies. It is one of the largest breweries in the world, with an annual brewing capacity of 14 million barrels of beer per year (16.4 million hectoliters). This brewery is located on a 100-acre site in St. Louis, Missouri, USA.

The new ammonia refhgeration plant has a nominal capacity of 17,000 tons (59.8 MW) of refrigeration (TR). The plant equipment is driven by nearly 20,000 horsepower (14.5 MW) of electric motors.

The refrigeration equipment is installed in a two story, 44,000 ftz (4,088 m’) Compressor Hall building.

The Compressor Hall supports the following brewing refrigeration operations: stockhouse cooling and dehumidification, product cooling, water chilling, secondary refrigerant cooling, and space air conditioning, Flooded ammonia is used in all evaporators.

Compressor Hall Project

The Compressor Hall project started out as a “blue sky” idea to build a state of the art ammonia refrigeration plant to replace an old, outdated, unreliable, and costly ammonia plant. The old ammonia plant included equipment identical to that used at the 1904 St. Louis Worlds Fair. The equipment age ranged from 72 years old to 25 years new.

The old refrigeration plant was becoming increasingly unreliable in support of the highly automated brewing and packaging production facilities. High operating costs and environmental issues paved the way for changing the “blue sky” idea into reality. Engineering of the Compressor Hall project started in 1992. The plant was commissioned and placed in full service in 1996.

The Old Ammonia Refrigeration Plant

The old ammonia plant comprised of: horizontal, double acting, low speed reciprocating compressors, wooden cooling towers, horizontal and vertical water cooled condensers, and other auxiliary equipment. The compressors were powered by synchronous DC motors. The old ammonia plant had undergone many expansions over the course of several decades with equipment installed in five separate buildings.

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The old plant capacity was around 10,500 TR (37 MW), powered by 18,000 horsepower (3 1.4 MW). The system operated on dual suction pressures, with a common discharge pressure. The old plant operated on lower suction pressure than the current plant. The low suction pressure was 22 psig, 8°F (1.5 bar, -13.3"C). The capacity of the old plant reflected the old operating conditions. The control system consisted of panel board unit controllers with limited automation capabilities.

Vibration, noise, and ammonia leaks made the plant feel and smell like an ammonia plant. The ammonia compressors were fitted with an elaborate exhaust system around the packing glands that directed ammonia releases to a large ammonia scrubber using chemical neutralizing agents. This system reduced the airborne levels of ammonia in the operating spaces. Without this system, ammonia exposure limits would have been exceeded. Several truck loads of ammonia were purchased periodically to make up for routine ammonia losses.

The New Refrigeration Plant

The new refrigeration plant contains main ammonia equipment, auxiliary equipment, and a central control system.

Main Ammonia Equipment

1. Three suction traps. 2. Twelve ammonia screw compressors. 3. Twelve evaporative condensers. 4. Six high pressure liquid ammonia receivers. 5. Three liquid ammonia sub-coolers.

Auxiliary Equipment

The following auxiliary equipment operates in conjunction with the main ammonia equipment: 1. Six liquid ammonia pumps. 2. Three pump out compressors. 3. Two ammonia distillers. 4. Ammonia scrubber. 5. Central oil delivery tank and pump. 6. Central oil removal system. 7. Cooling water pumps, tank, chemical treatment for the evaporative condensers. 8. Ventilation equipment.

Control System

A fully automated Digital Control System (DCS) controls, monitors, and collects

220 operating data from a remote control room.

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Design & Operational Features of the Main Ammonia Equipment

Ammonia Suction Traps

There are three 12 ft diameter (3.7 m) suction traps (Figure 1). Two operate on low suction pressure and one operates on high suction pressure. The three suction traps can be cross- connected and operated at a single suction pressure.

The suction traps are installed in the ammonia system to prevent liquid carryover to the compressors. They separate the liquid entrained with the vapor stream returned from the evaporators. They also ensure that only vapor is drawn into the compressors. This protects the compressors from damage due to liquid slugging. The suction traps were designed to effectively separate the liquid and promptly remove this liquid out of the traps. The suction pipes connecting the evaporators to the suction traps are also fitted with drain pots to act as primary liquid traps. This reduces the chances of liquid carryover closer to the source (evaporators).

The suction traps were designed for optimum separation velocity of vapor, diameter, minimum height of liquid, and configuration of inlet and outlet piping. Historical design data and equations listed in ASHRAE refrigeration handbook were used for the design of the suction traps.

Piping Arrangement

Ammonia suction pipe headers entering and exiting the suction traps are arranged to effectively remove entrained liquid. The inlet pipes are turned 90 degrees downward, and the outlet pipes are turned 90 degrees upward inside the suction traps. This arrangement ensures that any wet vapor changes direction twice inside the traps before the vapor enters the compressors. The design of the suction traps also assures that separation velocity and liquid heights are within safe limits.

Ammonia Compressors

The twelve ammonia compressors are twin screws, of the same make and model. Compressors operate on 30 psig, 16.5"F (2.07 bar, -8.6"C) and 45 psig, 30°F (3.1 bar, -l.l°C) suction. Each compressor is rated at 13 15 TR - 1620 TR (4.6 MW - 5.7 MW) depending on the operating suction and discharge pressures. Each compressor is powered by a 1,500 hp (1,119 kW) electric motor. The compressors incorporate the following:

Thermo-Syphon Oil Cooling

Compressor oil is cooled using ammonia as a coolant employing the thermo-syphon principle. Liquid ammonia flows inside the tubes and the oil flows in the shell of shell and tube heat exchangers. Liquid ammonia flow varies based on heat load. Oil flow is regulated by a

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three way thermostatic mixing valve to maintain the desired oil temperature. Liquid ammonia is supplied to the oil coolers from the high-pressure liquid receivers which are located on the second floor above the oil coolers. A liquid distribution header supplies the liquid ammonia to all oil coolers from the lower portions of the liquid receivers. Similarly, a central distribution header returns ammonia from the oil coolers to the top of the high-pressure receivers.

To ensure unrestricted ammonia flow to the oil coolers, pipes were sized for a 4: I overfeed rate and low pressure drop.

Oil Pumps

Cycling oil pumps are used on all compressors to conserve energy. The oil pumps cycle off when pre-set differential pressure across the compressor is reached. Four compressors are equipped with full time cycling oil pumps to allow for a "black" plant start up.

Oil Charging

Compressor lubrication oil is pumped from a bulk oil storage tank to charge each compressor through a hard piped oil-charging header. The clean oil tank is sized to hold the oil charge of three compressors. This design eliminates oil handling at each compressor, thus reducing the chance of oil spills and eliminating personnel safety issues.

Oil Removal and Disposal

Oil is removed from the ammonia compressors into two central oil receiver/distiller tanks through a hard piped oil removal header. This design eliminates oil handling at each compressor thus reducing the chance of oil spills.

Side Port Economizer

The new ammonia compressors are equipped with side port economizers. Ammonia vapor is supplied to the side port economizers from three shell and tube ammonia sub-coolers. These coolers sub-cool the liquid ammonia supplied to the evaporators. The side port economizers increase the efficiency of the ammonia plant by 3% to 4% (Curve 1).

Piping is designed to insure that clean and dry ammonia vapor is introduced into the compressor cavity through the economizer port. A strainer insures a supply of clean vapor to the economizer port.

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Compressor Discharge Piping

All compressors discharge hot gas into common hot gas headers connecting the compressors to the condensers and receivers. Two discharge isolation valves are installed on each compressor to assure high confidence of isolating a compressor from the common hot gas headers. A check valve is installed on each compressor's hot gas header to prevent back flow. Because most of the ammonia hot gas headers are installed outdoors, liquid condenses inside these headers during cold temperatures and reduced flow. The hot gas headers are sloped and fitted with low point drain pots to drain and collect the condensed liquid. Level switches installed on the pots warn operators of liquid ammonia accumulation in the pots and energize electric heaters installed around the pots to boil off any liquid ammonia.

Compressor Suction Piping

Six 24-inch suction headers connect the compressor suctions to the three suction traps. Branch pipes to the compressors are connected to the top of the main header. The main headers are equipped with low point drain pots to assure that only dry gas is supplied to the compressors.

Ammonia Evaporative Condensers

The twelve evaporative condensers installed are induced draft, of the same make and model (Figure 2). Each condenser is fitted with two 40 hp fans and two 7.5 hp circulating water pumps. The condensers are spaced on the building roof to reduce short cycling. Each condenser is equipped with two sump mounted water-circulating pumps. All condensers are connected to common ammonia hot gas, ammonia liquid drain, ammonia purge, water-distribution and water drain headers.

The evaporative condensers are designed to control the ammonia condensing temperature to 95°F (35°C) with an ambient wet bulb temperature of 78°F (25.6"C). The evaporative condensers were carefully evaluated to select the optimum number of condensers to match the cooling loads. A balance was evaluated to either select more compressors operating at high head pressure, and fewer condensers; or fewer compressors operating at low head pressure and more condensers (Curves 2,3,4,5).

Ammonia vapor and liquid headers are designed to insure unrestricted flow to and from the condenser coils. Condenser inlet pressures are equalized between the condensers and the receivers. The liquid piping from the condensers is sized and routed to ensure proper drainage from the condensers to the receivers. Each liquid drain from a condenser coil is fitted with a P-trap to balance the flow of gas between all condensers. Non-condensable gases are removed from condenser coils promptly though the use of an automated purging system. Water quantities and chemical treatment are controlled and monitored in proportion to load changes.

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High-pressure Liquid Receivers

Six vertical high-pressure liquid ammonia receivers are installed on the second floor below the evaporative condensers and above the ammonia compressors (Figure 3). These receivers are designed to function as combined thermo-syphon drop receivers and liquid storage receivers. Liquid ammonia is drained by gravity from the condensers into the receivers. The bottom volume of the receivers is piped to insure a constant supply of liquid ammonia to compressor oil coolers. Return piping from the oil coolers is elevated above the receivers to ensure proper separation of gas from the thenno-syphon return headers into the receivers. The remaining volume of the receivers supplies liquid ammonia to the evaporators.

The liquid ammonia receivers are equipped with low and high level switches and level indicators. The low-level switch alarms if the liquid level drops below the level required for the oil coolers. The high level switches alarms if the level builds up and affects the free vapor space.

Liquid Ammonia Sub-Coolers

High-pressure liquid ammonia is sub-cooled prior to distribution to the evaporators. The liquid ammonia sub-coolers are shell and tube heat exchangers (Figure 4). Ammonia supplied from the receivers to the evaporators flows though the tubes and is sub-cooled by a split stream that flows through the shell side. The evaporated gas from the shell side is fed to the economizer ports on the compressors at an intermediate pressure of 67 psig (4.6 bar).

The liquid ammonia is sub-cooled to prevent flashing in the ammonia headers as many of the evaporators are a great distance from the Compressor Hall and at higher elevations. This insures that all evaporators are supplied with only liquid ammonia and not gaseous ammonia. In addition, sub-cooled liquid increases the refrigeration system efficiency. A number of existing evaporators were sized for sub-cooled liquid flow (Curve 6).

The vapor generated in the ammonia sub-cooler is supplied to the economizer of the compressors. The suction pressure of the ammonia sub-cooler is regulated by the economizer port pressure. If the ammonia sub-cooling load exceeds the flow capacity of the economizers, the excess ammonia vapor is transferred to the suction of the compressors.

Ammonia sub-coolers are equipped with level switches on the surge drum to guard against carry over of liquid ammonia into the economizer gas headers. If the level of liquid ammonia in the sub-cooler reaches a high level, the economizer port feed valves are signaled to close. This avoids slugging compressors with liquid.

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Liquid Ammonia Distribution Headers

The sub-cooled high-pressure liquid ammonia is distributed to the evaporators in two 8 in (200 mm) insulated pipe headers. Each header can be automatically isolated to stop the supply of liquid ammonia in the event of a major release. The sub-headers can also be isolated automatically to stop the supply of liquid ammonia to the evaporators. Relief valves are installed on liquid ammonia headers fitted with automatic shut off valves to relieve any hydrostatic pressure.

Main Ammonia Suction Pipe Headers

Dozens of suction headers connect the evaporators to three main suction headers: two 30 in (762 mm) and one 24 in (610 mm). Each header is piped to a low point liquid collection pot to trap entrained liquid at the source. The collection pots are fitted with liquid level switches, and electric heaters. When the liquid ammonia level builds up to the marked level, the electric heater is energized to boil off the liquid. If the liquid level builds up to a high level mark, an alarm is indicated in the central control room signaling unusual liquid carry over. High liquid levels can be pumped out of these traps before the liquid reaches the main suction traps.

Ammonia Hot Gas Headers

The ammonia hot gas headers connect the compressors, condensers and receivers equalizing system pressure. System pressure is monitored and controlled from a central sensing point on the equalizing headers.

Relief Valves

Relief valves installed on all heat exchangers are vented to the low-pressure suction headers. Relief valves vented to atmosphere are fitted with low-pressure (2 psi, 0.14 bar) burst disc indicators that are wired to a control panel. If an atmospheric relief valve leaks or lifts, the burst disc ruptures and indication is provided to the control room identifying which relief lifted and at what time it lifted.

Dual relief, pilot operated valves with inlet selector valves are used on equipment that can not easily be taken out of service to maintain a relief valve.

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Auxiliary Equipment

Liquid Ammonia Pumps

Six electric piston driven, positive displacement liquid ammonia pumps are used to transfer liquid ammonia from the low-pressure suction traps to the high-pressure liquid receivers.

Two design features are incorporated in the piping design in order to reduce the chance of the pumps becoming vapor-bound. The suction of the pump is vented to the gas side of the suction trap and a solenoid valve is installed between the suction and discharge of the pump to equalize the pressure across the pump when the pump cycles off.

Ammonia Purgers

Automatic purgers are installed to remove non-condensable gases from the ammonia condenser coils and receivers. A purge connection is installed on the liquid outlet pipe of each condenser and in the gas space of each receiver. All purge points are piped to a refrigerant type purger. Purge points are monitored and cycled from the refiigeration control system.

The actual ammonia liquid pressure/temperature are compared to theoretical values to verify the performance of the purgers.

Ammonia Pump Out Compressors

Pump out compressors are installed to pump ammonia out of the equipment and piping during maintenance. The pump out compressors are water cooled reciprocating compressors. The cooling water is drained from the compressor cooling jackets when the compressor stops to prevent freeze damage. Discharge from the compressors can be directed to the ammonia suction headers or to atmosphere to minimize the amount of ammonia released to atmosphere and to prevent the discharge of air into the ammonia system.

Ammonia Scrubber

A single packed tower water scrubber is connected to the discharge of the pump out compressors to prevent venting ammonia to the atmosphere. The scrubber is simple and effective in removing ammonia from the gas stream. The ammonia is absorbed into water and discharged to the brewery’s wastewater treatment plant.

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Ammonia Distillers

Two carbon steel vessels with external steam heating coils are used to boil off ammonia from the ammonia-laden oil drained into the distillers from the various evaporators (Figure 5). Ammonia recovered from the oil is vented into the system. The ammonia-free oil is then pumped into tanker trucks for proper disposal.

The amount of oil routinely drained from the refrigeration system has been greatly reduced with the installation of the new screw compressors. This has reduced the manpower cost of draining oil from evaporators, increased the efficiency of the evaporators, reduced the cost of replacement oil and reduced the cost of oil disposal.

Central Oil Charging System

A 1,500-gallon (5,678 liter) tank, pump and distribution pipes are installed to charge oil to each compressor from a central location. This system allows for the bulk delivery of compressor oil and eliminates the manpower cost and hazards of handling 55-gallon oil drums.

Evaporative Condenser Water

A continuous flow of water is supplied to each evaporative condenser to make up for water lost due to evaporation, and drift. Water overflows continuously to each condenser sump to maintain a consistent water quality in all condenser sumps.

The overflow water then flows through a central tank located on the first floor of the Compressor Hall. From this tank the water is pumped back to the evaporative condenser sumps. At the pump discharge the water is run though a mechanical strainer and chemical analyzers. Water treatment chemicals are injected as needed to maintain the proper water chemistry to prevent corrosion, scale formation and microbiological activity in the cooling water.

The local condenser water circulating pumps circulate the water from the condenser sump over the ammonia coils. This insures proper flow distribution over the entire ammonia coil.

Chemical Treatment

Chemical treatment is supplied to the condensers in proportion to the condenser load. The chemical treatment system provides corrosion protection, controls bacteriological growth, and assures heat transfer surfaces are clear of scale build up. Blow down is regulated to control the total dissolved solids in the water. Central bulk tanks and pumps are installed to deliver the chemicals into the system.

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In an effort to minimize corrosion potentials, the evaporative condenser sumps are made of 304 stainless steel, and the central water tank is made of fiberglass.

Ammonia Sensors

Ammonia sensors are strategically located throughout the building to sense ammonia. The sensors are connected to the building control and safety systems. The sensors activate the building ventilation system to evacuate the building if ammonia levels exceed 50 ppm. The control panel for the ammonia sensors is located outside the building. In case of ammonia leaks, the operators can determine the location of high ammonia concentrations.

Building Ventilation

Outside air is used to ventilate the building and to remove the heat generated by equipment (Figure 6). The outside air flow supplied to the building is regulated between minimum and maximum levels. The minimum level ensures that the outside air meets requirements set by ASHRAE 15 guidelines for the ammonia plant. The maximum level is set by the outdoor temperature and refiigeration plant load profile. Power for the ventilation equipment add up to 320 hp (239 kw). A control scheme is employed to cycle the ventilation equipment based on the outdoor air temperature and projected load profile.

The amount of outside air introduced into the building was estimated to maintain maximum indoor temperature of 104°F (40°C), based on the 1 'YO ASHRAE summer design temperature, and actual heat generation.

Control System Overview

The ammonia system is fully automated in all aspects; yet, flexibility is built into the system. The control system ties compressor microprocessors into a custom Distributed Control System (DCS). The following highlights the functions achieved by the DCS system:

Overall Ammonia Plant

The DCS control system provides the following functions for the overall ammonia plant: 1. Maintain suction pressure. 2. Set and maintain head pressure. 3. Optimize plant operation. 4. Evaluate on line equipment and demand for refrigeration. 5. Integrate equipment to achieve optimum performance. 6. Compare measurements to equipment design. 7. Monitor liquid inventory.

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Compressor Control

Compressors operating on dual suction pressure are fitted with shut off valves and limit switches connected to each pressure. The limit switches provide assurance, through the control system, that the compressor is lined up to the required suction headers. When the control system acknowledges that the compressor is lined up to the desired suction pressure, compressor control set points are automatically reset.

The DCS operates in conjunction with the compressor controllers to provide the following: 1. Start, stop compressors. 2. Monitor all operating parameters. 3. Rotate compressors. 4. Maintain cycle time. 5. Optimize compressor loading and unloading based on system loading, performance. 6. Stop compressor if the liquid reaches a dangerously high level in the suction trap. 7. Reduce demand charge.

Condenser Control

The DCS control system operates the condensers as follows: 1. Start, stop fans and pumps. 2. Regulate make up water into each sump. 3. Regulate cycle time. 4. Set head pressure. 5. Maintain head pressure. 6. Purge coils of non-condensable.

Liquid Ammonia Receivers

1. Monitor liquid level in receivers. 2. Alarm when liquid level is low, or high.

Liquid Ammonia Sub-Coolers

1. Controls liquid ammonia feed to the sub-coolers. 2. Monitors liquid level in the sub-coolers. 3. Monitor ammonia temperatures and pressures.

Safety

1. Monitor wind speed and direction. 2. Monitor ammonia levels inside the building. 3. Monitor progression of liquid carry over from the unit coolers.

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Energy Management

1. Determine head pressure set point based on outdoor wet bulb temperature. 2. Optimizes compressor loading and unloading. Ensures maximum number of compressors are

fully loaded. 3. Operate all system components at the best efficient conditions. 4. Measure and calculate on line capacity and electric power consumption. 5. Display on-line hp/TR.

Process Safety Management (PSM )

PSM was followed every step of the way. Detailed analysis of each process was completed from the inception to the completion of the project: 1. HAZOP analysis was completed during the early phases of the design. 2. Employees participated in all phases of design, transitioning, and commissioning of the new

systems and decommissioning of the old system. 3. Conducted detailed pre-start up safety reviews. 4. Every participant was trained on PSM.

Coordinating New & Old Systems

Detailed planning was completed to maintain the old ammonia plant in operation while building the new plant. Planning included the following: 1. Installation of cross tie pipes and valves on each system. 2. Providing temporary cooling to critical process areas. 3. Installing by-pass pipe connections to provide cooling to the critical areas. 4. Utilizing the pump out pipe network to supply liquid, or hot gas to the critical areas. 5. Making pipe tie-ins during cold weather in order to lessen the effects of ambient conditions

on the process. 6 . Devising back up plans to address unpredictable conditions. 7. Carrying out the tie ins over the course of two winter seasons while the major components of

the plant were being designed and built.

Challenges

We faced difficult challenges every step of the way during this project. The following are some of these challenges: 1. Transfer service to the new plant, while operating the old plant. 2. Test pipe connections at tie-in points. 3. Keep air out of the operating system. 4. Prevent ammonia releases to atmosphere.

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5. Make tie-ins on large pipes located on outdoor bridges, 90 feet up in the air. 6. Maintain safe practices. 7. Isolation valves. 8. Sizing criteria for relief valves. What to size compressor relief valves for: process flow, fire?

At what condition? 9. How to interpret code requirements. Whose interpretation should be followed? 10. How to apply best engineering practices? Whose engineering practices: In-house resources,

outside resources from vendors, colleagues in the industry, colleagues, members of IIAR? 1 1. Test pressures at system boundaries to test new piping. Duration of test.

Decommissioning Old Ammonia Plant

The old ammonia plant decommissioning involved: 1. Severing all connections between the operating ammonia plant and old plant. 2. Removing ammonia from equipment and piping. 3. Ensuring that no detectable traces of ammonia residues remained in pipes, or equipment. 4. Carefully demolish the old equipment. 5. Carefully handle, remove, and dispose of tremendous quantities of wooden structures

saturated with chemicals from the old cooling towers.

Conclusion

1. Transferred cooling from the old refrigeration plant to the new refrigeration plant without interruption to the brewery’s production.

2. Charged 50 tons of ammonia into the new system. 3. No reportable release of ammonia at any stage of the project. 4. Virtually eliminated fugitive emissions due to use of welded pipes and valves. 5. Operating a simple, flexible, and efficient refrigeration plant. 6. The success of this major undertaking was attributed to dedicated teams from plant operation,

and corporate engineering.

23 1

ILLUSTRATION & SYSTEM PERFORMANCE CURVES

Illustrations

Suction Trap Piping Arrangement Evaporative Condenser Piping Arrangement High Pressure Liquid Receiver Piping Arrangement Liquid Sub-cooling Piping Arrangement Ammonia Distillers Piping Arrangement Building Ventilation

System Performance Curves

Compressors

Economizer Effects

Evaporative Condensers

Evaporative Condenser Capacity Profile, Wet Coils Evaporative Condenser Capacity Profile, Dry Coils

Overall System Performance

System Condensing Requirements Optimum System Performance

Evaporators

Evaporator Flow: Sub-cooled Vs non Sub-cooled liquid

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EF-231-R-6 EXHAUST FAN RF-231-R-2

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