Southeastern Regional Biomass Energy Program

Heat-Activated Cooling Devices: A Guidebook For General Audiences

Administered For The United States Department of Energy

Tennessee Valley Authority Environmental Research Center Biotechnology Department Muscle Shoals, Alabama 35662-1 01 0

NOTICE

This report was prepared as an account of work sponsoreb by an agency o the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommen- dation or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Heat-Act ivated Cooling Devices

Prepared by

George Wiltsee Appel Consultants, Inc. 25554 Longfellow Place

Stevenson Ranch, CA 91381

February 1994

Prepared for the Southeastern Regional Biomass Energy Program (SERBEP)

The Tennessee Valley Authority, Muscle Shoals, Alabama administers SERBEP for the U.S. Department of Energy

SERBEP Project Manager Phillip C. Badger

CONTENTS

Section page

1

2

3

4

5

6

7

8

9

10

Introduction .. Systems and Components ................................................................... 1

Feasibility of Heat-Activated Cooling .......................................................................... 11

Biomass Conversion to Refrigeration ......................................................................... 12

System Costs ..................................................................................................................... 14

System Integration ........................................................................................................... 15

Permits and Regulatory Agencies ................................................................................ 16

Selecting a Contractor ..................................................................................................... 19

Case Studies ....................................................................................................................... 20

References .......................................................................................................................... 23

Glossary .............................................................................................................................. 24

.. 11

TABLES

Table

Fuel Used in Air Conditioning a 10. 000 Square Foot Building for a Season ..... 1

Heat -Activated Cooling Systems ................................................................................. 2

Biomass Heating Values and Moisture Contents .................................................. 12

Estimated Refrigeration Produced from Wood-Fired Boilers ............................ 13

Emission Levels Considered Significant Under PSD Regulations .................... 16

Allowable PSD Increments ......................................................................................... 17

U.S. Environmental Protectiaa Agency Regional Offices ................................... 18

Comparison of Desiccant Based System with a Conventional System ............. 22

iii

FIGURES

Figure page

1 Absorption refrigeration system .................................................................................. 3

2 Steam jet ejector chiller ................................................................................................. 4

Solid desiccant air conditioning cycle ......................................................................... 6

Hybrid desiccant cooling system used on a supermarket ....................................... 6

Heat-activated cooling system costs .......................................................................... 14

iv

1

INTRODUCTION == SYSTEMS AND COMPONENTS

What is heat-activated cooling and how does it reduce costs? Heat-activated cooling is refrigeration or air conditioning* driven by heat instead of electricity. A mill or processing facility can use its waste fuel to air condition its offices or plant. Using waste fuel in this way can save money. Otherwise the air conditioning system would use electricity, and the plant or mill would pay a waste disposal fee. Heat-activated cooling is an alternative to generating electricity with the waste fuel.

Most refrigeration systems use a "vapor compression" cycle. An electric motor powers a compressor. Early refrigeration systems used heat instead of electrical or mechanical inputs. Modern versions of these systems are available today. The heat source may be a flame, hot water, or steam. When biomass residue is the fuel, steam usually is the heat source.

The amount of fuel required to air condition a building for a year depends on factors such as equipment performance, building construction, and weather. Table 1 shows the typical operating hours of an air conditioner per season for some cities in the southeastern United States. It also shows the approximate fuel use and electricity savings to cool a 10,000 square foot building for a season in these cities. In Birmingham, for example, a mill would use up to 283 tons of residue during the cooling season. This would save over 99,000 kilowatt-hours (kWh). At 4c/kWh, the mill would save about $4,00O/year on its electric bill.

Table 1 Fuel Used in Air Conditioning a 10,000 Square Foot Building for a Season

City Hours Birmingham, AL 1,200 - 2,200 Charlotte, NC 700 - 1,100 Columbia, SC 1,200 - 1,400 Little Rock, AR 1,400 - 2,400 New Orleans, LA 1,400 - 2,800 St. Joseph, MO 1,000 - 1,600

Fuel, tons Electricity, k W h 154 - 283 54,100 - 99,100 90- 141 31,500 - 49,600 154- 180 54,100 - 63,100 180 - 308 180 - 360 129 - 206

63,100 - 108,000 63,100 - 126,000 45,100 - 72,100

* The term "refrigeration" is used in this booklet in the general sense, to mean the production of cooling effect. In a more limited sense it can also mean process cooling at temperatures well below the freezing point of water (32 "€9. Most of the technologies discussed in this booklet are not applicable to low-temperature refrigeration (see Table 2).

1

Introduction -- Systems and Components

The four basic types of heat-activated cooling systems available today are:

Absorption cycle Desiccant system Steam jet ejector Steam turbine drive

Table 2 summarizes key features of these systems.

Table 2 Heat-Activated Cooling Systems

System

Capable of Chilled Water Steam Cooling or Air Pressure

below 32 OF ? Conditioner? Required cos t

Absorption: - Lithiumbromide No cw 15 psig Lowest - Ammonia Yes cw 15 psig Prohibitive

Desiccant No NC 15 psig High

Steam jet No cw >lo0 psig High

Steam turbine Yes cw >lo0 psig varies

The most widely used of these four cycles is the absorption system. Steam and hot water commonly activate absorption systems. They can adapt to any existing steam distribution system. If an existing heating, ventilating, and air conditioning (HVAC) system is not a chilled water system, modification is necessary. Absorption systems only come as water chillers.

Of the two absorption systems, only the ammonia absorption cycle can refrigerate below 32 OF. Ammonia systems cost too much to be practical. They have very large heat exchange surfaces and require custom engineering and fabrication.

Desiccant systems remove moisture from the air. They also can filter the air. Integration into an existing system requires major changes to the ducting. N o one yet offers a packaged unit using steam or hot water. This may change soon. Developers have been working on desiccant systems because of their many advantages. So far they custom design these systems, usually combined with conventional refngeration.

____

Process industries use steam jet ejectors widely for process refrigeration. They are economical when low-cost fuel generates high-pressure steam. They have no moving parts other than water pumps. They provide reliable long-term service.

2

Introduction -- Systems and Components

Steam turbine drives often replace electric motor drives in chillers and refrigeration compressors. When low-cost high-pressure steam is available, it can effectively provide air conditioning or refrigeration. For low-temperature refrigeration service, turbine drive is the only serious alternative.

Absorption Systems The name of this cycle describes how it works. A fluid (the sorbent) absorbs

another fluid (gaseous refrigerant) coming from an evaporator. (See Figure 1.) The evaporator is where the cooling occurs. The sorbent "compresses" the refrigerant by absorbing it at low temperature and desorbing it at high temperature and pressure. Lithium bromide systems use a lithium bromide solution as the sorbent and water as the refrigerant. A pump pressurizes the solution into a generator where the refrigerant boils off. This is where the heat that runs the system enters.

Generator eat Rejedion

Condenser Heat h

Figure 1. Absorption refrigeration system

A condenser condenses the refrigerant vapor (steam). The condenser cooling water evaporates in a cooling tower. This is where the heat leaves the system. The high-pressure condensate expands to a lower pressure through an expansier device. In the evaporator, well below atmospheric pressure, the condensate boils at a low temperature. Evaporation absorbs about 1000 Btu /Ib from the water, reducing its temperature.

A single-effect unit has one generator. It operates on 15 pounds per square inch guage (psig) steam or hot water. A double-effect unit has two generatr -s in series. It is more efficient and uses 30-40% less energy per ton of refrigeration, It requires 11 4 psig steam. Commercially available single-effect, lithium bromide absorption chillers have capacities from 3 to 1,660 tons.

3

Introduction -- Systems and Components

Steam Jet Refrigeration The steam jet ejector is a good method of producing refrigeration where high

pressure steam is available at low cost. Its widest use is in industrial processes. It has no moving parts except the pumps that are common to all chiller systems. Maintenance requirements are low. Many machines have been in continuous service for 20 to 30 years. The equipment has a high overload capacity. It is free of vibration, light, and can easily be located on a roof. It is an older system, not extensively used in today's market. Its primary disadvantage is that it operates under strong vacuum, requiring careful maintenance.

The best applications are in concentration or drying of heat-sensitive foods and chemicals. Cooling produced by the evaporation reduces the processing temperature and prevents product deterioration. Concentrating fruit juices, freeze- drying food, dehydrating antibiotics, crystallizing chemicals, and chilling le-afy vegetables are typical examples.

The system has an evaporator, a primary steam jet ejector, a condenser, and a secondary ejector to remove non-condensables from the condenser. (See Figure 2.) High-pressure steam accelerating through the primary ejector draws water vapor from the evaporator. The pressure in the evaporator (also called a flash tank) is 0.15 pounds per square inch absolute (psia). At this pressure, water boils at 45 OF. The 55 O F water returning from the air conditioning equipment boils the 45 O F water.

The condenser condenses the mixture of steam and flash vapor from the primary ejector. Most of the condensate returns to the boiler. Some goes back to the chilled water loop. The secondary ejector removes any air that enters the system.

No n co nd e ns ab k r

I - - C > cooling 1 " . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , .*::: . . . . . . . . . . . . . .

I

Figure 2. Steam jet ejector chiller

4

Introduction -- System and Components

With 100 O F condensing temperature and 45 OF chilled water temperature, a steam consumption of 26 lb/ hr per ton of cooling is typical. In comparison, the st am consumption of a single effect lithium bromide absorption chiller is 18 Ib/hr per ton at a steam pressure of 15 psig. The steam consumption of a double-effect lithium bromide absorption chiller is 10 Ib/hr per ton.

Desiccant Systems In hot, dry climates people have long used evaporative cooling to provide

comfort air conditioning. The so-called "swamp cooler" is a simple system that evaporates water into a hot, dry ventilation air stream. The temperature of the air stream drops as it evaporates the water. In humid climates a desiccant can get the same results. The desiccant removes most of the water vapor in the ventilation air. It also removes dust, pollens, and bacteria or viruses. A heat exchanger cools the dry air before it enters the "swamp cooler". A heat source regenerates the desiccant for reuse in a cyclic process.

There are two basic types of desiccants, solid and liquid. Solid materials like silica gel, activated alumina, or molecular sieves adsorb water vapor by virtue of their structure. These materials have billions of tiny pores, with very large surface area. As air passes through, water molecules move from the air to the desiccant. Liquid desiccants such as triethylene glycol have a lower vapor pressure than water. When air contacts the glycol, water condenses from the air.

Both liquid and solid desiccants need a heat source to regenerate them after they have taken on moisture. This heat can come from steam or hot water produced in a biomass boiler. Desiccants regenerate at lower temperature than lithium bromide/water mixtures. There is not much experience with high temperature regeneration of desiccants, such as that offered by steam or hot water from a biomass boiler.

Figure 3 shows a typical desiccant air conditioning cycle. A rotary wheel dehumidifier containing a desiccant dries and heats ambient air. The dry air cools in a rotary heat exchanger and then cools further in a "swamp cooler" before entering the building. Exhaust air cools in another evaporative cooler, then heats up in the rotary heat exchanger and a steam or hot water heat exchanger. The hot, damp exhaust air regenerates the desiccant in the rotary wheel dehumidifier.

Solid, rotary bed desiccant daumidifiers are widely available for industrial dehumidification applications. Off-the-shelf units use steam or hot water for regeneration. These state-of-the-art units can become the basis for packaged air conditioners when incorporated into a unit that includes heat exchangers, blowers, and controls. N o manufacturer currently o f f ~ s a true air conditioning package based on solid or liquid desiccant dehumidification.

5

Introduction -- Systems and Components

- Cod Dry-

I

/ I \ Moist*

Figure 3. Solid desiccant air conditioning cycle

Exhaust Heat Exchanger ,c

J 4 Wprm Dsmp - -

Hybrid systems -- combining a desiccant system with a standard vapor compression refrigeration cycle -- can be very efficient. The vapor compression cycle can operate at a higher evaporator temperature since it doesn't have to condense moisture. This improves its performance. The desiccant has less moisture to remove than in a desiccant-only system, allowing a lower regeneration temperature. Figure 4 shows the application of a hybrid desiccant cooling system to a supermarket.

Evaproative Cooler => Water

1

/I\ - Cold * D m

- 6 Heat 25.000 cfm

Exhaust source I -

Rotary Desiccant

Ventilation (3750 cfm)

Rem Heat Evaporative Cooler

coil - 4 - 5

air I t UT

I I U Air

conditioner

Figure 4. Hybrid desiccant cooling system used on a supermarket

Exfiltration (3750 cfm)

Transmission load

6

Introduction -- Systems and Components

Most applications of heat-activated cooling will involve retrofitting existing systems that already contain conventional air conditioning equipment. Integrating a desiccant system with an existing vapor compression air conditioning system should be straightforward. The dehumidification equipment can be located in the ventilation duct.

Steam Turbine Drives You can use a steam turbine instead of an electric motor to drive the

compressor in a conventional air conditioning or refrigeration system. Installing a turbine is more costly and complex than installing an electric motor. The refrigeration portion of the system is identical. It must use an open-drive chiller or refrigeration compressor. In an open-drive system the shaft extends out of the compressor. It connects to the shaft of an electric motor, steam turbine, gas turbine, or reciprocating engine. (A hermetic compressor, in contrast, can only use an electric motor drive. It has one housing enclosing both the electric motor and the compressor.)

Open-drive packaged chillers usually have reciprocating compressors in the smaller sizes and centrifugal compressors in the larger sizes. Open-drive centrifugal chiller packages are available in sizes ranging from 150 to 500 tons. When equipped with an electric motor, the unit cost ranges from $225/ton for the smaller units to $200 /ton for the larger units. Cost of the electric motor ranges from $23 to $36/ ton.

The best choice of refrigeration compressors driven by steam turbines is the screw compressor. The twin-screw compressor is most common. The single-screw compressor is a new entry. Screw compressors have advantages over reciprocating compressors such as smaller size, fewer moving parts, and low vibration levels.

A hydraulically actuated slide valve controls the capacity of the screw compressor. The valve reduces the length of the space in which the rotor accepts suction gas. The suction volume ranges from 100% down to 10% of maximum. Capacity changes in proportion, and the system remains stable. As with any compressor, a variable speed drive is an effective method of changing capacity. Since most screw compressors can operate comfortably in the speed range of 1,800 to 4,500 revolutions per minute (rpm), steam turbine drives with variable speed throttles work well.

Steam turbines often drive blowers, compressors, and exhausters in steel mills, and paper machines in paper mills. Turbine-driven boiler feedwater pumps often handle large flows and high heads in industrial applications. The variable speed capability, low maintenance, and high reliability make them the preferred drive for high capacity requirements.

Steam turbines come in various configurations -- single and multiple stage, condensing, noncondensing, and extraction. Where the size is not too great and

7

Introduction -- Systems and Components

efficiency is not an essential requirement, plants generally use single-stage turbines. The performance of a steam turbine depends mainly on the conditions of the inlet steam and the exhaust steam. The design of the boiler sets the turbine inlet conditions (steam pressure and temperature). If the boiler does not contain a superheater, the inlet temperature is the saturation temperature, determined by the steam pressure. The important exhaust condition is the pressure. The requirements of the downstream process equipment, or the need for high efficiency, set the exhaust pressure.

A noncondensing or backpressure steam turbine is in the steam line directly between the boiler and the steam load(s). It generates power (or drives the compressor) only when there is a demand for steam by the process equipment. For example, the steam entering the turbine might be at 250 psi& and the process steam leaving the turbine might be at 15 psig. The steam rate of a noncondensing turbine drive chiller is about 40 lb/hr per ton of refrigeration. This is about double the steam rate of a single-effect absorption chiller or a condensing turbine drive chiller. The noncondensing turbine drive for chiller applications is not a good choice.

In a condensing steam turbine system, the steam that flows through the turbine condenses immediately as it leaves the turbine exhaust. Condensation creates a powerful vacuum as it dramatically reduces the volume of the steam. The pressure drop across the turbine is greater than in the noncondensing turbine. This delivers more power, and results in a steam rate of about 22 lb/hr per ton of refrigeration.

The condenser serves two purposes -- to condense and recover steam exhausted from the turbine and to .provide a vacuum for the turbine exhaust. Recovery of the exhaust steam reduces the makeup water requirements to 1-5%, instead of 100%. The performance gains from the vacuum exhaust are well worth the cost of the additional equipment.

Barometric condensers work by mixing exhaust steam with cold water. Surface condensers work better. They are shell and tube heat exchangers which keep the condensing steam separate from the cooling water. Air can be removed from the condensate, which returns to the boiler feedwater system. Recirculating the condensate reduces corrosion and scaling in the boiler.

Air removal is the most important factor in condenser performance. If air is not removed, the condenser becomes airbound and the pressure rises. Steam- powered ejectors remove the air from the water.

A condensing steam turbine cycle must reject heat from the condensing steam. The latent heat of vaporization of water is about 1000 Btu/lb. Cooling water absorbs this heat and then dissipates it to the air. Methods which evaporate the water are more effective and use smaller equipment. The cross-flow cooling tower is the dominant method.

8

Introduction --Systems and Components

Cool Storage Cool storage reduces the peak energy demand by spreading the air

conditioning load on the refrigeration system over the entire day. A typical system chills the storage medium during periods $of off-peak cooling demand (e.g., in the early morning before working hours). Then, when the building needs space cooling during peak demand periods, the only energy needed is to run fans and pumps. The refrigeration system can be smaller -- sized to meet the average cooling load, not the peak. There are good reasons to use cool storage as part of a heat-activated cooling system:

To reduce the initial investment in the fuel preparation and feed system, boiler, steam distribution, heat rejection and refrtgeration systems.

To meet the air conditioning needs of offices, warehouses, or manufacturing areas. These facilities impose high peak cooling requirements for a few hours a day and little or no demand during nonworking hours -- an ideal situation for cool storage.

To provide refrigeration during periods of low steam availability, when other process loads suci 2s dry kilns need steam.

“Ple most comvron cool storage systems use ice or chilled water. They consist of one or more stov 3e tanks, circulation pumps, an evaporator, and piping and valving to the co01in~~ coils. A pump circulates chilled water to cooling coils when needed. The warmed water from the cooling coils returns to the tank.

Biomass Boilers The wood products industry has well-proven technology for using wood fuel

in boilers. In the firetube boiler, combustion gases flow through tubes submerged in water in a pressure vessel. In the watertube boiler, the water flows through tubes heated on the outside by hot gases. Generally, in plants requiring boilers with a steam capacity of more than 25,000 lbjhr and 125 psi& watertube boilers are more economical.

Watertube boilers may be either packaged or field built. Packaged boilers have steam capacities up to 50,000 Ib/hr. Field built, industrial watertube boilers have steam capacities up to 600,000 lb/hr. The steam produced may be low pressure saturated steam or superheated steam with pressure to 2,400 psig and temperatt - to 1,000 OF. Typical steam conditions in small industrial plants are about 150 to 50C sig and 366 to 725 OF. For small applications requiring less than 125 psig and less tnan 25,000 Ib / hr, firetube boilers may be desirable.

9

Introduction -- Systems and Components

The four most commonly used furnace designs for wood firing are pile burners, stoker grate boilers, fluidized-bed boilers, and suspension burners. Pile burners are simple and can handle very moist fuel with large quantities of dirt and debris. They are less efficient than other boiler types and need to be shut down

380,000 lb/ hr of steam, in configurations varying from one to six cells. periodically for cleaning. Modern pile burning systems range from 15,000 Ib/hr to

-

Stoker fired boilers with grates are the leading type of boiler design for wood firing. The grates may be sloped, flat, moving or stationary, and made of either cast iron or refractory brick. Moving grates provide better control over the burning than stationary grates. Moving grates can automatically discharge ash. Spreader stokers feed fuel to the furnace pneumatically. Stokers are not very flexible to changes in fuel quality. Variations in ash, particle size distribution, and moisture content cause operating problems.

-___--

A fluidized-bed boiler has a steel plate with holes in it at the bottom. Air blown through the plate suspends a hot bed of sand and fuel in a boiling motion. The fuel burns at a lower temperature than in conventional boilers, which reduces NO, emissions. Fluidized beds can burn difficult fuels such as agricultural residues better than other types of boilers.

Suspension burners fire dry sawdust and shavings in various configurations that create cyclonic turbulence. Suspension firing requires fuel moisture to be less than 15% and fuel particle size to be less than 1 / 4 inch. Dry fine fuel particles create a potential explosion hazard.

10

2

FEASIBILITY OF HEAT-ACTIVATED COOLING

Heat-activated cooling is probably cost effective for you if

You have waste that is causing disposal problems or expense (a captive fuel source)

You have a use for refrigeration or cooling in-house

You have a steady, year-round steam use in-house or close by

Your first task is to find out whether heat-activated cooling is a good idea for your site. If you hire an enpeer ing consultant to help with the initial feasibility study, he or she will go through the following steps:

A site visit to obtain preliminary information. This plus the consultant's experience will suggest if heat-activated cooling could be successful at your site.

A screening study that will include evaluations of

- Site data; financial information; fuel and electricity costs - Fuel quantities (by month) and qualities (heating value, moisture, ash) - Energy usage; monthly electric bills; cooling requirements; growth plans - System sizing fuel available; boiler and cooling system size - System type; equipment, engineering, insurance, and operating costs - Cash flows; electricity savings; plant costs - Economics; payback period; discounted cash flow analysis

If the screening results are positive, the consultant will do a more detailed design and costing. This detailed engineering study will show whether the investment in a heat-activated cooling system will pay off for your facility.

11

3

BIOMASS CONVERSION TO REFRIGERATION

The amounts of steam used and refrigeration produced depend on the system design aniJ the biomass properties. Table 3 shows typical heating values and noisture ccmtents of different types of biomass.

Table 3 Biomass Heating Values and Moisture Contents

Moisture Fuel (% wet basis)

Bark 50 Whole tree chips 50 Sawdust 40 Planer shavings 10 Sanderdust 5 Cotton gintrash 10

Higher heating value, Btdlb (as received) (dry basis)

4000 8000 4250 8500 5 100 8500 7650 8500 8075 8500 6350 7060

Most species of wood and bark, when dry, have about the same chemical -omposition. The moisture content, size, and ash content vary over wide ranges, and influence the design of the plant. Sanderdust and furniture plant scraps contain the least amount of moisture of the wood fuels (less than 10%). These very dry fuels allow the highest boiler efficiencies. Bark from hydraulically debarked logs, or from trees in areas with high rainfall, and sawdust from mills using water-cooled saws, may contain 65% moisture or more. At such high levels, combustion becomes unstable, and the fire goes out. Hog fuel -- a mixture of green wood and bark -- normally contains 45 to 55% moisture.

Note that there are two ways to express moisture content -- the wet or the dry basis. Engineers usually calculate moisture from the as-received weight of the fuel; this is the wet basis. (This report uses the wet basis.) People in the wood products industries often calculate it from the dry weight. It is easy to convert from one basis to the other using the equations below. For example, 50% moisture (wet basis) and 100% moisture (dry basis) mean the same. Every pound of fuel contains a half- pound of water and a half-pound of bone-dry wood.

12

Biomass Conversion to Refrigeration

Wet basis moisture content = Dry basis moisture content divided by (1 + dry basis moisture content)

Dry basis moisture content = Wet basis moisture content divided by (1 - wet basis moisture content)

where the wet and dry basis moisture contents are eTressed as decimals.

Table 4 shows how much refrigeration can be produced from wood as a function of its moisture content, over the boiler size range of 150 to 1,000 horsepower (hp).

Table 4 Estimated Refrigeration Produced from Wood-Fired Boilers

Wood fuel, tonshr

Boiler size,

150 200 300 400 500 600 700 800 900

1,000

hP1 Dry2 Green3 Steam, lbhr

Refrigeration, tons4

0.47 0.62 0.94 1.25 1.56 1.88 2.18 2.50 2.80 3.12

0.87 1.15 1.74 2.31 2.89 3.48 4.03 4.62 5.18 5.78

5 170 6900

10,300 13,800 17,250 20,700 24,100 27,600 3 1,000 34,500

260 345 520 690 860

1,040 1,210 1.380 1 ;550 1,730

Note: 1. One boiler horsepower = 34.5 l b h of steam 2. One ton of dry fuel (10% moisture content wet basis) will make about 11,000

3. One ton of green fuel (50% moisture content wet basis) will make about 6,000

4. 20 lb/hr of steam will produce about 1 ton of refrigeration in a single effect

lb/hr of steam

l b h of steam

lithium bromide absorption system

13

4

SYSTEM COSTS

System costs are site-specific. Figure 5 shows the potential range of installed costs (in December 1992 dollars) for heat-activated cooling systems up to 2,000 tons of refrigeration. These costs are for complete plants -- fuel handling systems, boilers, steam systems, chillers, cooling towers, controls, and hookups. The cost range is very broad, depending on many factors.

1992 $ million

0 500 1000 1500 2000 Tons of refrigeration

Figure 5. Heat-activated cooling system installed costs in 1992 dollars

As the figure shows, the cost of a heat-activated cooling system increases as the system size increases. Unit costs (costs per ton of refrigeration) generally decrease due to economies of scale. The complexity of the design, and its integration requirements, greatly influence the cost of a system. Low quality fuel requires more screening and blending equipment, and sometimes requires more expensive combustion and particulate control systems. Site conditions (labor costs, limited space, etc.) also influence plant costs.

14

5

SYSTEM INTEGRATION

The two most important facility systems with which the heat-activated cooling device must interface are the steam distribution system and the heating, ventilating, and air conditioning (HVAC) system. If the system is being retrofitted to an existing facility, a great deal depends on the existing facility layout. Each site is unique, and systems must be integrated case by case.

The steam distribution system has two major elements: steam lines and condensate lines. When retrofitting to the steam distribution system, the primary consideration is whether the steam mains can be routed to the air conditioning or refrigeration equipment. (Or conversely, can the air conditioning or refrigeration equipment be located near the steam mains?) Chilled water can be distributed from chillers near the steam mains to the various air conditioning systems. Sorption systems, on the other hand, produce conditioned air and must be located near the space to be conditioned.

Absorption and desiccant systems can use hot water (condensate) or steam for the energy source. These systems can be installed on the condensate return lines. When using condensate, the pipe size will be larger than when using steam.

Integration with the HVAC system can be on the air side of the existing system or on the chilled water side. For example, a new chilled water coil can be inserted into the cabinet of the air handling unit in series with the existing coil. The new coil receives chilled water from the heat-activated chiller. The feasibility of this approach depends on several factors:

The availability of space within the air handling unit The presence of a second condensate drain Sufficient static pressure capability of the fan

15

6

PERMITS AND REGULATORY AGENCIES

To install a new boiler you must obtain a Permit to Construct, a Permit to Operate, and possibly other permits, depending on your state and local requirements. If you are in an area that meets National Ambient Air Quality Standards (NAAQS), you must meet Prevention of Significant Deterioration (PSD) regulations. You must submit a PSD permit application if the plant will emit more than 100 tonslyear of a criteria pollutant or if the plant will emit pollutants at levels considered "significant" (see Table 5). As a general rule, emission rates from small wood-fired boilers (ie., boilers producing less than about 50,000 lb / hr of steam) will be below the rates shown in Table 5. If this is your situation, you will not need to file a PSD permit application. Hire a knowledgable consultant to advise you on permitting issues.

Table 5 Emission Levels Considered Significant Under PSD Regulations

Emissions Rate Pollutant (tondyear)

Carbon monoxide 100 Nitrogen oxides 40 Sulfur dioxide 40 Particulate matter 25

In the permit application, you must provide an air quality modeling analysis to assess impacts on NAAQS and allowable increments (see Table 6). You may have to provide one year of baseline air quality data if no data exist that meet EPA requirements. Submit the permit application to an EPA regional office, which will review the application and issue a permit. Table 7 lists the ten regional EPA offices.

PSD requires the use of Best Available Control Technology (BACT). BACT may take ?e form of a specific control technology or an emission limitation. For control cr articulate emissions from biomass boilers, BACT requires electrostatic precipitators or fabric filters.

16

Permits and Regulatory Agencies

Table 6 Allowable PSD Increments

Maximum Allowable Increase Pollutant (Micrograms per cubic meter)

Class I* Class I1 Class I11

Particulate matter Annual geometric mean 24-hour maximum

Annual arithmetic mean 24-hour maximum 3-hour maximum

Sulfur dioxide:

5 19 37 10 37 75

2 20 40 5 91 182

25 5 12 700

*Class I -- National parks, wilderness areas, national memorial parks Class 11 -- All other areas except Class 111 (most areas in U.S. are Class It) Class 111 -- Heavy industrial areas

Areas that have not met NAAQS are "nonattainment". If you are in one of these areas, you are not subject to PSD requirements. Major emission sources in these areas must:

Arrange for emission reduction from existing sources in the region that more than offset the total emissions of the new plant, and

Meet the Lowest Achievable Emission Rate (LAER) for the nonattainment pollutant. LAER is the lowest emission level met in practice or required by any state.

*

The Southeastern Regional Biomass Energy Program has a guidebook entitled "Permits-Regulations for Biomass Energy Facilities in the Southeast". It will help you plan your project by identifying permit requirements. It lists the regulations, permits, and standards for air quality, water quality, solid waste, safety, noise, and zoning/land use. It also lists agencies and services in the southeastern U.S. To obtain the guidebook, contact SERBEP a t

Tennessee Valley Authority P.O. Box 1010 Muscle Shoals, AL 35660 205-386-3086 fax: 205-386-2963

17

Permits and Regulatory Agencies

Table 7 U.S. Environmental Protection Agency Regional Offices

EPA Regional Office, Air Programs Branch States Included in Region

1.

2.

3.

4.

5 .

6.

7.

. 8.

9.

John F. Kennedy Federal Building Room 2303 Boston, MA 02203 617-223-6883

Federal Office Building 26 Federal Plaza New York, NY 10007 212-264-2517

Curtis Building Sixth and Walnut Streets Philadelphia, PA 19 106 215-597-8175

345 Courtland, NE Atlanta, GA 30308 404- 88 1 -3043

230 South Dearborn Chicago, IL 60604 3 12-353-2205

First International Building 1202 Elm Street Dallas, TX 75270 214-767-2745

324 E. Eleventh Street Kansas City, MO 64106 8 16-374-597 1

1 f 50 Lincoln Street Denver, CO 80295 303-837-347 1

215 Fremont Street San Francisco, CA 94105 4 15-556-4708

10. 1200 Sixth Avenue Seattle, WA 98101 206-442- 1230

Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, Vermont

New Jersey, New York, Puerto Rico, Virgin Islands

Delaware, District of Columbia, Maryland, Pennsylvania, Virginia, West Virginia

Alabama, Florida, Georgia, Mississippi, Kentucky, North Carolina, South Carolina, Tennessee

Illinois, Minnesota, Michigan, Ohio, Indiana, Wisconsin

Arkansas, Louisiana, New Mexico, Oklahoma, Texas

Iowa, Kansas, Missouri, Nebraska

Colorado, Montana, North Dakota, South Dakota, Utah, Wyoming

Arizona, California, Hawaii, Nevada, Guam, American Samoa

Washington, Oregon, Idaho, Alaska

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7

SELECTING A CONTRACTOR

To select a qualified contractor, identify some candidates, check references, get recommendations, and conduct interviews. Ask the leading candidate to do an initial screening analysis of your site. If the results make sense and look good, ask the consultant for a preliminary system design and cost estimate.

There is no such thing as a "free analysis". Equipment vendors and utilities will offer to pro ;de analyses at no cost. Remember that these sources are not the business of providing consulting services.

The equipment vendor seeks to sell boilers, turbines, and refrigeration equipment. Any analysis that it provides is only a part of that sales effort.

Utility personnel may be biased to preserve purchased power sales.

A list of heat-activated cooling system design/ build/installation contractors is available from SERBEP.

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8

CASE STUDIES

The case studies that follow illustrate two different situations that were favorable for heat-activated cooling systems using biomass fuel. The specifics of ycsr situation will differ from these. If you have some of these conditions at your wood processing or manufacturing plant, then heat-activated cooling may make sense -- and money -- for you.

La-Z-Boy Tennessee La-Z-Boy Tennessee in Dayton, Tennessee is one of five plants owned by La-

Z-Boy Chair Company. The plant produces 1,900 units per day of chairs, sofas, sofa sleepers, and reclining sofas. La-Z-Boy buys 12 million board-feet per year of green boards (mostly soft maple). Two 350 kW back pressure turbines provide 15 psig steam to kiln-dry these boards. About one-third of the incoming wood becomes sawdust, shavings, and wood scraps. A hog sizes the fuel and a pneumatic system conveys it to silos.

P: wiously, a small boiler disposed of waste wood and provided some space and dry kiln heat. In 1985, La-Z-Boy ?stalled a new 30,000 lb/hr (300 psig) wood waste-fired water tube boiler. Two singie-stage, back pressure steam turbines power two 350 kW synchronous generators and a 1,150 ton steam activated absorption chiller.

The plant uses about 65% of its wood waste for fuel. It landfills the balance at no cost. The landfill uses the dry wood waste as kindling to burn brush and other wood waste.

One operator on each shift watches the boiler fuel handling system, chiller, and turbine/ generators. Very little ash accumulates in the combustion chamber of the suspension burner. Operators manually clean out ash about once a month. They dispose of ash by land application on the owner's property.

Electric generation depends on plant steam load. Normally one turbine operates at a time. This provides 10 15% of inhouse electric needs. This saves $5,000-7,000 per month at a 5@/kWh retail electric rate. (1985 dollars)

20

Case Studies

The original air conditioning system used rooftop packaged units that provided heating with a steam coil and cooling with a direct expansion coil. Conversion to chilled water cooling involved replacing the steam coil with a hot water/ chilled water coil and disconnecting the compressor and condenser fan. The chiller produces 42 OF water for cooling. A steam converter produces 120 O F water for heating.

The two pipe distribution system requires switchover as demand changes from heating to cooling. For 2-3 weeks in the spring and fall, operators switch from one mode to the other mornings and afternoons. The switch involves some manual operation and takes 10-15 minutes.

The system has worked well. An initial problem after installing the boiler system was the lack of operator training. La-Z-Boy had no one with experience in wood-fired boiler operation, or experience with turbine / generators or absorption chillers. Provisions for training in the original contracts would have eliminated this problem.

Operators had problems with the automatic control system. The boiler was too Slow to respond to the chiller startup. A combination decrease in boiler response time and increase in chiller startup time alleviated this problem. The feed water control valve could not react fast enough for a sudden steam load demand. Failure to increase the feed water rate led to low-water boiler shutdown. This created problems with combustion controls.

The total installation cost about $1.4 million (1985 dollars). The 30,000 Ib/hr boiler system cost $500,000. This included auxiliary equipment from the feedwater pump through the char reinjection system. The 350 k W turbine/generator sets cost $55,000 each. The 1,150 ton steam-activated lithium bromide absorption chiller, bought used, cost $30,000. A similar chiller now costs $200,000 (about $174/ton). The cooling tower cost $25,000. Both fuel storage silos were in place before the modification. A new 76 ft. by 24 ft. diameter concrete silo would cost $100,000.

Payback of the $1.4 million took about 2 to 2.5 years. Without the boiler, wood waste probably would go to the landfill. This would cost $5.00/ ton because the quantity was greater than the landfill could accept. A limited market for industrial wood fuel exists in the local area at about $lO.OO/ton. Based on these projected disposal costs, the value of wood waste fuel to La-Z-Boy is $l.OO/million Btu. The alternate fuel, natural gas, is available for $4.90/million Btu.

La-Z-Boy is happy with this system and uses similar cogen/ heating/ cooling systems in their other five plants. The company is now expanding the Dayton facility by 270,000 square feet. This will increase their production rate t o 3,000 unitsjday. They will add a new 35,000 lb/hr wood waste-fired boiler and a second 1,150 ton absorption chiller. The existing turbine/generators are big enough to use

21

Case Studies

the additional steam. The new boiler will allow use of all waste wood plus waste cardboard and pallets generated onsite.

Semco Manufacturing, Inc. Semco Manufacturing, Inc. is a manufacturer of rotary heat exchangers and

desiccant wheels. Semco installed a demonstration unit in a wood products manufacturing facility in the Southeast. The system cools and dries 16,000 standard cubic feet per minute of air to air condition the plant. A wood-fired boiler burning kiln dried scraps and wood residue provides steam for regeneration of the desiccant.

A study conducted by Semco produced the economic analysis in Table 8. The desiccant system cost $297,000 to install and $14,00O/year to operate (1992 dollars). This compares with an estimated $255,000 to install, and $34,00O/year to operate, a conventional air conditioning system. The desiccant system, because of its operating cost savings, paid out in about two years cimpared to a conventional system. Semco projected that the desiccant system would come down in installed cost to about the same level as the conventional system. At that point it would be clearly preferable.

Table 8 Comparison of Desiccant Based System with a Conventional System

(Cost Estimates, 1992)

quipment cost Installation cost

Total installed cost

Packaged Open Cycle Projected Open Conventional Desiccant Cycle Desiccant

System System System

$98,000 $160,000 $1 19,000 157,000 137,000 137,000

$255,000 $297,000 $256,000

Operating cosdyear

Payback period, years

$34,000 $14,000 $14,000

2 0

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9

REFERENCES

Elliott, Thomas C. 1989. "Standard Handbook of Powerplant Engineering". McGraw-Hill Publishing Company, New York.

Guinn, Gerald R. 1992. "Design Guide for Thermally Activated Air Conditioning". Prepa -ad by the University of Alabama in Huntsville for the U.S. Department of Energ> joutheastern Regional Biomass Energy Program, October 1992. (This report is the primary source for the information contained here. Figures 1-4 came from this reference.)

Guin Geiald R. 1990. "Design Manual for Small Steam Turbines". Prepared by the University of Alabama in Huntsville for the U.S. Department of Energy Southeastem Regional Biomass Energy Program, March 1990.

Jahn, Larry G., and R. Neal Elliott 111. "Wood Energy Guide for Agricultural and Small Commercial Applications". Published by the North Carolina Agricultural Extension Service. Sponsored by the U.S. Department of Energy Southeastern Regional Biomass Energy Program.

Southeastern Regional Biomass Energy Program. 1986. "Case Studies of Biomass Energy Facilities in the Southeastern U.S." Prepared by Meridian Corporation, August 1986.

Southeastem Regional Biomass Energy Program. 1986. "Permits-Regulations for Biomass Energy Facilities in the Southeast". Prepared by Nero and Associates, Inc., August 1986.

The Technology Application Laboratory of the Georgia Institute of Technology Engineering Experiment Station. 1984. "The Industrial Wood Energy Handbook". Van Nostrand Reinhold Co., Atlanta, Georgia.

Tennessee Valley Authority. 1991. "Biomass Design Manual; Industrial Size Systems". Tennessee Valley Authority, Renewables and Special Projects, Reprint 1991.

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10

GLOSSARY

Ash -- non-combustible fraction of a fuel.

BA CT -- Best Available Control Technology; air emissions control technology mandated by Federal regulations.

Baghouse -- a chamber fitted with fabric filters that collect solid material in the flue gas from boiler exhaust.

Boiler horsepower (bhp) -- the equivalent of heat required to change 34.5 pounds per hour of water at 212 OF to steam at 212 OF. It is equal to a boiler heat output of 33,475 Btu / hr.

Btu -- British thermal unit; a unit of heat equal to 252 calories. The quantity of heat required to raise the temperature of one pound of water from 62 OF to 63 OF.

Electrostatic precipitator -- A particulate collection device that uses high-voltage electricity to charge particles in the gas stream, which migrate by electrostatic attraction to grounded steel plates where they adhere. The collected particles are dislodged by rapping the plates and fall into a collection hopper.

Rue gas -- all gases and products of combustion that leave a furnace by way of a flue or duct.

Fuidized bed -- air blows through a sand bed to bubble or entrain the sand.

Fy ash -- Fine solid particles of non-combustible ash carried out of a furnace by the draft.

Heating value -- of a fuel is the heat generated when 1 pound of fuel burns completely. Higher heating value (HHV) is the heat generated when one pound of fuel is burned completely and the water formed or vaporized during combustion is condensed to release the latent heat of vaporization. It is easily measured in a bomb calorimeter.

Lower heating value (LHV) is the heat generated when the water is not condensed, as occurs in practical applications such as aroilers and engines where the combustion

24

Glossary

gases leave as a vapor. LHV is difficult to measure. Therefore, HHV is commonly used in the United States to designate the heating value of fuels. The LHV, the usable heat, depends on the type of fuel and its moisture content. For green wood it is about 18 percent lower than the HHV; for bone-dry wood it is about 6.2 percent lower. In calculating power requirements using HHV, keep in mind that the fuel will provide only the heat of the LHV.

Hog -- a machine for reducing the size of wood slabs, edgings, bark, and other material. Two types of hog exist: knife types chip the wood, and hammermills beat or grind the wood against a screen or spaced bars to reduce its size. Hog fuel is the sized product from the hog.

Payback -- a method to see whether it is worthwhile to invest in an item or a process that will increase income or reduce operating costs. The payback period is the number of years it will take for the investment to be recovered through cost savings or added income.

Sanderdust -- extremely fine waste wood product from a plywood mill.

Scrubber -- an apparatus for removing impurities and contaminants from gases by use of water or a dry granular medium.

Silo -- an air-tight building used to store wood fuel under certain conditions.

Spreader stoker -- a device that throws or blows fuel into the firebox of a boiler so that it spreads evenly over the grate.

Suspension burner -- a device to burn fine particles of wood turbulently mixed with forced air over the main fuel bed.

’ Ton of refrigeration -- equivalent to 12,000 Btu/ hr.

Turndown ratio -- the lowest load for which a boiler will operate efficiently.

Turnkey system -- the contractor designs, builds, and installs a complete system.

Volatile matter -- the fraction of a solid fuel that evolves as the fuel heats up. The volatile matter burns as a gas.

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