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THE KALINA CYCLE FOR CEMENT KILN

WASTE HEAT RECOVERY POWER PLANTSMark D. MirolliChief Technology Officer

Recurrent Resources, LLC

Abstract

Cement production is one of the most energy intensive industrial processes in the world. In many worldregions, energy cost is 50% to 60% of the direct production cost of cement. Energy cost is incurred dueto the need for large quantities of thermal heat for the kiln, calcination and drying processes and electricalenergy for operation of motors for grinding mills, fans, conveyers and other motor driven processequipment.

The Kalina Cycle utilizes the waste heat from the cement production process to generate electricalenergy with no additional fuel consumption, and reduces the cost of electric energy for cementproduction. The thermal efficiency improvement of the Kalina Cycle is 20% to 40% in comparison withconventional waste heat power plants that utilize the hot gases available in a cement plant.

A Kalina Cycle power plant offers the best environmentally friendly alternative for power generation fromlow-grade waste heat. It maximizes kW-hrs generated using a closed loop system to recover heat forelectricity production without hazard to the environment. The Kalina Cycle uses a mixture of ammoniaand water as its working fluid; a common solution used extensively world wide for refrigeration plants. Inthe event of an accidental release, ammonia is considered a biodegradable fluid. It does not contribute tophotochemical smog, global pollution or global warming; and will not deplete the ozone layer. Its use asan industrial fluid is well documented with a proven track record for safety in industrial plants.

This paper is a summary of Kalina Cycle Technology for cement plant waste heat applications. Specificplant designs are referenced to present a summary of the power plant systems and to describe thefinancial advantages of the Kalina Cycle waste heat power plant to the cement plant owner.

Background

In many countries, energy costs represent the largest component of direct production cost for cement.Energy cost represents as much as 50% to 60% of cement direct production cost. Energy cost isincurred due to the need for large quantities of thermal heat for the kiln, calcination and drying processesand electrical energy for operation of motors for grinding mills, fans, conveyers and other motor drivenequipment. Although the fuel use and energy use will depend on the type of process, equipment andsystem efficiency, and fuel heating value, typical requirements for coal use is in the range of 150-250 kg

per metric tonne of cement, and typical requirements for electrical energy use is in the range of 80-125kWhr per metric tonne of cement. The Kalina Cycle can use the waste heat from the cement productionprocess to generate electrical energy with no additional fuel consumption, and reduce the cost of electricenergy for cement production.

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Table 1

WORLDWIDE CEMENT INDUSTRYAND ELECTRICAL ENERGY USE

(2000 PRODUCTION)

World Market:

World Cement Production 1.7 billion tons per year

Average Electricity Requirement 100 kWyr/ton

Total Electricity Energy Requirement 170 billion kWhrs/year

Equivalent Capacity (80% PLF) 24,300 MW

Major Producing Countries:

China 575 million tons per yearIndia 95 million tons per yearUnited States 92 million tons per yearJapan 77 million tons per yearRepublic of Korea 50 million tons per yearBrazil 41 million tons per yearThailand 38 million tons per yearGermany 37 million tons per yearItaly 35 million tons per year

The Kalina Cycle

The Kalina Cycle is a new thermal cycle for energy conversion for electric power generation thatimproves the efficiency of energy conversion and specific capital cost ($/net kW) of waste heat toelectricity conversion in cement plant applications. The increased thermal efficiency and the specificthermodynamic advantages of the Kalina Cycle for low temperature heat sources makes it well suited forindustrial Waste Heat Recovery (WHR) power generation applications, allowing a higher generatingcapacity for a given heat source than can be achieved with the conventional Rankine steam cycle ororganic Rankine cycle plants.

The Kalina Cycle is an energy conversion process utilizing a working fluid mixture of ammonia-water in aclosed-loop arrangement to maximize electricity output from an existing waste heat source. Thecomponents of the Kalina Cycle are proven industrial equipment ensuring a reliable and trouble-free plantoperation without interfering with the cement production process.

The Kalina Cycle advantage over the Rankine cycle varies inversely with the temperature of the heatsource. The temperatures of the heat sources (preheater and clinker cooler exhaust streams) for atypical cement facility are in the range, 200

oC to 400

oC. With this temperature range, the Kalina Cycle is

20% to 40% more efficient than the Rankine Cycle. This means that a 20% to 40% larger power plant ispossible with the Kalina Cycle. The capital cost for a Kalina Cycle power plant is comparable to that of aRankine cycle power plant. The primary advantage is the ability to get more electrical energy from theavailable heat source, and therefore achieve a greater annual savings in energy cost.

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The Kalina Cycle process uses a binary working fluid of ammonia and water in a closed-loop cycle. Akey feature of the technology includes the ability to vary the ammonia-water concentration throughout thepower plant system to optimize energy conversion, and to add heat recuperative stages for increasedefficiency. The use of ammonia permits efficient use of waste heat streams allowing boiling of theammonia-water working fluid to start at lower temperatures. The use of a binary fluid allows thecomposition of the working fluid to be varied through the use of distillation, providing a richerconcentration through the heat acquisition stage (Heat Recovery Vapor Generator) and leanercomposition in the low-pressure condenser. Since the molecular weight of ammonia is close to that ofwater, a standard back-pressure, multi-stage turbine-generator is used.

A typical process schematic for a Kalina Cycle waste heat recovery power plant for a cement facility isshown in Figure 1. The heat sources are the preheater exhaust and the clinker cooler exhaust gases.Two Heat Recovery Vapor Generators (HRVGs) are provided, one for the preheater exhaust (stream 25-26) and one for the cooler exhaust (stream 43-46). A rich mixture of water and ammonia is boiled andsuperheated in the HRVGs and the superheated vapor is expanded through a back-pressure turbine(Point 31). The turbine exhaust is too rich (high ammonia concentration) to condense, so it is then cooledand diluted with the bottoms from a vapor separator/demister, and is then fully condensed in the lowpressure condenser (Stream 18-1). At this stage, part of the working fluid is sent to the vaporseparator/demister through recuperative heat exchangers and part of the working fluid is mixed with thehigh ammonia concentration vapor stream from the vapor separator/demister. This process restores the

working fluid to the optimum ammonia-water concentration for the heat acquisition stage of the cycle. Theworking fluid is then condensed in the high pressure condenser (stream 13-14) and returned to theHRVGs.

The Distillation and Condensation Sub-System (DCSS) consists of the demister/separator, recuperativeheat exchangers, high and low pressure condensers and control system. It provides the vital function ofestablishing the high ammonia-water concentration for the heat acquisition stage and a low ammonia-water concentration at the condensation stage.

The DCSS technology is a key component for the high efficiency of a Kalina Cycle plant for industrialwaste heat applications. The distillation process leans out (i.e. lowers the ammonia concentration of) theturbine exhaust stream just prior to the low pressure condenser. Since a leaner mixture has a lowersaturation pressure at a given temperature, the exhaust stream will then condense at a lower pressure. A

lower turbine exhaust pressure increases the pressure expansion of the working fluid through the turbine,thus maximizing turbine power.

All heat input for the distillation process is acquired only from the turbine exhaust stream. This process ispossible because of the variable temperature boiling and condensing feature of an ammonia-watermixture. This process will not work for pure working fluids such as water or hydrocarbons because thesepure fluids boil and condense at a constanttemperature.

The second stage of the DCSS restores the working fluid to the original ammonia-water concentration. Afeedpump then directs this fluid back to the HRVGs to repeat the process in a closed-loop arrangement.

A mixture of ammonia and water is used as a working fluid for several reasons:

First, the use of a lighter component (ammonia), allows efficient use of the waste heat stream at ahigher pressure by causing boiling to start at lower temperature.

Second, the use of a mixture allows the composition to be varied through the use of distillation,such as the richer composition through the boiler, with the leaner composition in the low pressurecondenser. The variable temperature boiling process of ammonia-water reduces losses in heattransfer processes throughout the power plant, thereby increasing the efficiency of the powercycle.

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Third, because of the similar molecular weight of ammonia versus water (17.03 vs. 18.01) theammonia-water vapor behaves virtually the same as steam, which allows the use of standardsteam turbine components.

Fourth, standard materials can be used. Carbon steel and standard high temperature alloys areacceptable for handling ammonia. Only the use of copper and copper alloys is prohibited in

ammonia service.

Fifth, ammonia is readily available and relatively inexpensive.

Sixth, ammonia is not harmful to the environment.

Seventh, there are proven safety procedures for the handling and use of ammonia in industrialplant applications.

Additional project design and operating features of the Kalina Cycle for Waste Heat Recovery (WHR)power plant applications that are especially applicable for cement plant projects include the following:

Design of the WHR power plant is such that cement production will not be interrupted in the event

the power plant is shutdown, or trips off-line.

Freeze protection is not required for the working fluid.

There is no power plant liquid effluent (no boiler blowdown for once-through vapor generators).

The plant capacity will automatically follow the heat source deviation by a sliding pressureoperation mode.

The HRVGs are simple heat exchanger designs that do not require steam drums. This allowsfast cycling of the HRVG during startup and shutdown and increases the flexibility of the boilerdesign to minimize tube fouling caused by sticky dust deposits. Proven tube cleaning and dustremoval systems are part of the HRVG design.

Kalina Cycle Power Plant Capacity

The potential capacity of a Kalina Cycle WHR power plant for a cement facility will depend primarily onthe waste gas mass flow rate(s) and temperature(s). Factors that influence these parameters orotherwise affect the design capacity of the power plant include the following:

Cement production capacityFacility annual average capacity factorType of cement production processEfficiency of cement production processChemical composition of the waste gasesWater-cooled or air-cooled condensersDesign ambient temperature and humidityDiversions of waste heat for coal and limestone dryingPlant layout

Depending on the above parameters, a Kalina Cycle for a 3000 tpd kiln is expected to be in the range of6 MW to 9 MW net electricity generation. Specific examples of possible waste heat to energy conversionschemes are as follows:

Clinker cooler exhaust only (no preheater heat available for electricity production) of 607,500 lbs.per hr. and 649 F (343 C) to produce 3075 kW net electricity

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Preheater exhaust of 607,500 lbs. per hr. and 725 F (385C) and clinker cooler exhaust of263,250 lbs. per hr. and 680 F (360 C) to produce 10,000 kW net electricity

Multiple preheater exhausts (3 kiln operation) totaling 1,237,750 lbs. per hr. at 740 F (393 C) toproduce 11,100 kW net electricity

Final electrical production values will depend on a range plant operating conditions including the source

and temperature of cooling fluid and plant location.

Figure 1

TYPICAL KALINA CYCLEFOR A CEMENT KILN

25

26

30

31

38

16

17

18

1

2

8

7 3

415 10

11

12 19

56

13

14

21

22

23

58 5924

53

52

54 60 '

62 "

64

63

44

4542

46

65

61 '

43

Kalina CycleConceptual Flow Diagram

System 1-2A

KCS1-2

1

2 3

4 5 6

7 8

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Economics of Kalina Cycle Waste Heat Recovery Power Plant

The capital cost for a Kalina Cycle waste heat recovery power plant is expected to be comparable to thatof a Rankine cycle in terms of $/kW for a similar size power plant. The primary advantage is the ability togenerate more electricity, and thus achieve greater savings in facility energy cost. A hypothetical projectexample is helpful to explain the benefits of a Kalina Cycle WHR power plant.

An economic analysis is dependent on a large number of inputs and assumptions. These include projectdesign and operational data, financial data, capital cost estimates, and operating cost estimates.Reasonable assumptions of these are dependent on the specific project, its location, and its owner.

Assume that a 3000 tpd cement facility is using 100 kWhr/t and operates the equivalent of 100% capacityfor 300 days per year. The electrical energy use would be 90,000,000 kWhr per year. At $0.06/kWhr, theannual cost for purchased electricity would be $5,400,000. Assume the owner wants to reducedependence on the electricity grid by about 50% by building a 6 MW Kalina Cycle waste heat recoverypower plant inside the fence with a capital cost of $9,000,000 and operating cost of $0.003 to $0.004 perkWhr. The simple payback period for the WHR power plant is less than 4 years after accounting for theoperating and maintenance costs for the Kalina Cycle WHR power plant.

There are a number of possible project financing structures possible for this type of power plant

application including project debt financed and lease financed structures.

ECONOMIC ADVANTAGE DEPENDS ON:

Avoided Cost of Purchased or Captive Generated Energy Heat Source Temperature and Flow Heat Source Availability Annual Average Load Factor Size of Kalina Cycle Power Plant Capital Cost of Kalina Cycle Power Plant Capital Cost of Alternative Energy Source

Fuel Cost of Alternative Energy Source O&M and Overhaul Cost of Alternative Energy Source Financing Terms Escalation Tax Issues

Operation and Maintenance for the WHR Plant

A Kalina Cycle waste heat power plant built within a cement facility will not require additional operatingpersonnel. The controls of the waste heat power plant will be integrated with the cement plant controlsystem to prevent any possible impact of an upset situation on cement production. For example, a tubeleak in the HRVG would cause the power plant to be immediately isolated from the cement kiln.

Typical O&M costs for this type of power generation system are in the range of $0.003 to $0.004 perkWhr of net generation. Scheduled plant maintenance will be conducted during normal outages for thecement kiln. Short outages (less than one week) are typical for the first four years, with a major outagefor turbine and I&C system overhauls in the fifth calendar year of operation. The major outage is typically3 to 4 weeks duration. Over the 20 to 30 year life of the power plant, this five year O&M schedule willrepeat.

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Table 2

Waste Heat Power PlantTypical 5-Year O&M Schedule

Year: 1 2 3 4 5Equipment:

HRVG S S S S SKalina System S S S S STurbogenerator S S S S MCooling System S S S S SBalance Of Plant S S S S S

Electrical S S S S SI&C S S S S M

M: Major OverhaulS: Short Outage

CO2 Emission Benefits of the Kalina Cycle

The Kyoto Protocol on Global Warming is an historic agreement that will have significant impact on thecement industry. Initially, many countries will be asked to set voluntary reduction targets. Whether thesecountries responsibility will remain voluntary in the future or other pressure will be applied will depend toa large extent on the responsiveness and effectiveness of their programs for reduction of emission ofgreenhouse gases. In addition, the international agreements and regulatory facilities under developmentfor banking, sale and/or trading of CO2 offsets offers the cement industry a unique opportunity toacquire additional benefits through implementation of cogeneration projects that will offset CO2 emissionsfrom fossil fuel fired power generation facilities. If a waste heat recovery power plant energy generationreplaces purchases from the grid, a case can be made for demonstrating an offset of greenhouse gasemissions from grid power plants.

If we assume a coal consumption rate of 0.76 kg/kWhr, for electric power generation, this would result inemissions of 1.325 kg of CO2 per kWh of electricity generated. A 10 MW Kalina Cycle waste heat

recovery power plant operating at 85% load factor would therefore offset (reduce) 98,700 metric tons ofCO2 emissions per year. This could either be credited against possible future reduction requirementsfor the cement facility or sold on the international market for CO2 offsets.

Summary

The Kalina Cycle is a new technology that changes the project economics of converting cement kilnwaste heat into electricity. It offers a 20% to 40% performance improvement relative to conventionalwaste heat systems. The technology has been proven in a demonstration facility at hot gas temperaturesexceeding 535 C (1992 to 1997), and in use in other applications including steel production (1999) andhydrocarbon processing (2005). It can be readily integrated into the operation of industrial processeswithout causing a disruption in the in the manufacturing facility.

References

Mlcak, H. A., An Introduction to the Kalina Cycle, Proceedings of the International Joint PowerGeneration Conference, Book No. H01077-1996.

Mirolli, M. D. and Leibowitz, H., First Kalina Combined Cycle Plant Tested Successfully, PowerEngineering, May, 1997.

Iiyoshi, T. et. al., Introduction of a Power Generating System by Low Temperature Waste Heat Recovery(Kalina Cycle Power Generating System), 2000.

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