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Paper Number : DOE/METC/C-96/7248

Title: Advanced PFBC Transient Analysis

Authors: J.S. White (Parsons Power Group, Inc.) D.L. Bonk (METC) L. Rogers (METC)

Conference: Power-Gen 96 Conference

Conference Location: Orlando, Florida

Conference Dates: December 4-6, 1996

Conference Sponsor: Penwell Publications

)oov 2 0 I996

O S T I

DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

Disclaimer

This report was prepared as an account of work sponsored by an agency of 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 use- fulness of any information, apparatus, product, or process dmlosed, or represents 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, recommendation, 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.

ADVANCED PFBC TRANSIENT ANALYSIS

Jay S. White Parsons Power Group Inc.

Donald L. Bonk Morgantown Energy Technology Center

Luke Rogers Morgantown Energy Technology Center

ABSTRACT

Transient modeling and analysis of Advanced Pressurized Fluidized Bed Combustion (PFBC) systems is a research area that is currently under investigative study by the United States Department of Energy's Morgantown Energy Technology Center W T C ) . The object of the effort is to identify key operating parameters afkcting plant performan% and '

then quanti@ the basic response of major sub-systems to changes in operating cond&ons. PC-TRAX, a commercially available dynamic s o h a r e program, was chosen and applied in this modeling and analysis effort. PC-TRAX's software system includes a library of modular components that describe the appropriate dynamic behavior of standard power plant equipment such as pumps, compressors, and gadsteam turbine configurations. These modules are linked together, such that thermodynamic and hydrodynamic information flow between the individual modules, to emulate the overall plant configuration. Customized dynamic models have been developed using Advanced Continuous Simulation Language (ACSL) for non-standard components such as carbonizers, fluidized bed heat exchangers, fluidized-bed combustors, solids cooler, and other near-term components found in PFBC power plant systems. These customized ACSL-based modules have been interfaced with the standard TRAX code and used for

. on-line transient analysis of complete power plant configurations.

This paper summarizes and describes the development of a series of TRAX-based transient models of Advanced PFBC power plants. These power plants generate a high temperature flue gas by burning coal or other suitable fuel in a PFBC. The high temperature flue gas supports low-Btu fuel gas or natural gas combustion in a gas turbine topping combustor. When utilized, low-Btu fuel gas is produced in a bubbling bed carbonizer. High temperature, high pressure combustion products exiting the topping combustor are expanded in a modified gas turbine to generate electrical power. Waste heat from the system is used to generate and superheat steam for a reheat steam turbine bottoming cycle that generates additional electrical power. Basic controVinstrumentation models were developed and modeled in PC-TRAX and used to investigate off-design plant performance. System performance for various transient conditions and control philosophies was studied.

INTRODUCTION

PFBC is an efficient method of coal combustion and one of the advanced power concepts demonstrated in DOE'S Clean Coal Technology (CCT) Program. First Generation technology (PFBC-I) burns coal in a pressurized fluidized bed combustor (PFBC) to produce a high temperature flue gas referred to as vitiated air. High pressure combustion air is provided by a gas turbiie compressor. Particulate matter is removed and the high temperature flue gas stream is utilized in a modified gas turbiie expander to generate electrical power. Waste heat is recovered and used in a steam turbine bottoming cycle that generates additional electrical power. Advanced, or Second Generation, technology (APFBC) adds a bubbling bed reactor, or carbonizer, to convert a portion of the coal feed into a low-Btu fbel gas. High temperature vitiated air from the PFBC supports combustion of this &el in a topping combustor. High temperature, high pressure combustion products from the topping combustor are then expanded in a modified gas turbine. The addition of the low-Btu fie1 gas allows for increased working fluid temperatures in the expander and increased efficiency potential as compared to that of the PFBC-I technology. A hybrid of the two, the 1-1/2 Generation PFBC, utilizes natural gas rather than low-Btu &el gas in the topping combustor. Each of these combined Gcle

,

approaches will be referred to in this paper. !! !:(I APFBC PLANT DESCRIPTION

A simplified schematic of an Advanced PFBC power plant concept is presented in Figure 1. The shaded area of Figure 1 corresponds to first generation (PFBC-I) technology. The area bordered by the thin broken line corresponds to the Advanced, or Second Generation (MFBC) technology. The 1-1/2 Generation PFBC would be realized schematically by replacing the carbonizer he1 gas train with a natural gas stream. A generic system description that covers each of the three combined cycle designs is given below.

As-received coal is dried and pneumatically feed to the carbonizer vessel along with a calcium-based sorbent. The carbonizer is a bubbling bed reactor which operates at approximately 14 atmospheres and an elevated temperature of at least 1,6000F. In the carbonizer, coal is converted into a low-Btu he1 gas and char. The-calcium based sorbent is used to capture gaseous sulfbr species, such as HzS, generated by the carbonization reactions. Char and sorbent not entrained in the fuel gas steam exits through and overflow drain and is routed to the PFBC. The low-Btu &el gas is cleaned of particulate material and routed to the topping combustor.

Hot char and sorbent from the carbonizer is conveyed to the PFBC vessel. In some cases, as-received coal is dried and pneumatically feed to the PFBC vessel along with a calcium- based sorbent. The char/coal is burned in the PFBC to produce a high pressure, high temperature (1,600 OF) vitiated air stream. The PFBC is a two stage fluidized bed reactor. The primary combustion zone, situated at the extreme bottom portion of the vessel, burns lean and operates with a superficial gas velocity of approximately 8 Wsec.

The secondary combustion zone operates with excess air and has a superficial gas velocity of approximately 12 ft/sec. The secondary combustion zone is much longer than the primary zone and provides residence time for the sorbent reactions. The calcium-based sorbent is used to remove up to 95 percent of the SO2 generated during charkoal combustion. Waste heat from the combustion process is recovered through the generation, superheating, and reheating of steam in the fluidized bed heat exchanger wHE>.

Pressurized Fluidized Bed Combustion (PFBC) I

Carbonired Hot Gas Flmation - WFuelGas 1 PartialGasifier

Super clean, super efficient PFBCs

!!

Figure 1 : Simplified Schematic of APFBC Power Plant Concept

High pressure, high temperature vitiated air exits the top of the PFBC vessel. The exiting gas stream entrains a large volume of solid material. The solid material typically consists of ash, fresh sorbent, sulfided sorbent, and unconverted carbon. Most of the solid material is removed by high efficiency cyclones. Any remaining solid material is removed in the downstream candle filter vessel. Solid material removed by the cyclone bank is routed to the FBHE. Although a majority of this material is directly returned to the PFBC, a portion is cooled prior to recirculation. This cooling of the PFBC solid material is the primary means of PFBC temperature control. Heat is recovered in the FBHE by generating and superheating steam. Heat transfer surfaces consist of submerged tube bundles, submerged enclosure wall surface, and exposed wall surface.

Solids-free high temperature vitiated air supports combustion of either low-Btu fuel gas or pressurized natural gas fuel in the topping combustor. Hot topping combustor flue gas

products are used to generate electrical power in a modified gas turbine (G/T) expander. Waste heat available in the expander exhaust is recovered in a heat recovery steam generator (HRSG). This thermal duty, along with that recovered in the FBHE, is used to generate additional electrical power in a steam turbine ( S / T ) bottoming cycle.

MODELING APPROACH

PC-TRAX is a commercial software tool that allows for the dynamic analysis of fossil- based power plants. PC-TRAX is the primary tool used in this analysis and was chosen because it is capable of dynamically describing most of the components found in APFBC power plant concepts. PC-TRAX consists of a library containing a several sets of modules that describe the dynamic behavior of standard commercial power plant equipment. The individual modules are linked together to obtain the desired plant configuration. Standard PC-TRAX modules were used to model all of the plant control hardware, the gas turbine expander, most of the steam turbine bottoming cycle, as well as all of the plant valving.and piping.

Customized dynamic modules were developed to describe the dynamic behavior of the :: near-term process components such as the carbonizer, PFBC, FBHE, and ash croler.

Language (ACSL) and dynamically interfaced with the standard PC-TRAX modules. The customized ACSL modules are supported by FORTRAN subroutines that are used to perform non-dynamic calculations such as physical property routines. Most of the mathematical models used to develop the customized ACSL code are based on prior work completed by PARSONS and Foster Wheeler Development Corporation[ 11.

The customized dynamic models were coded in Advanced Continuous Sim d ation

A transient model of a complete commercial-sized power plant must incorporate the thermodynamics, hydrodynamics, and chemistry in sufficient detail to provide accurate performance results during steady-state and transient operation. Additionally, the model must account for mass and energy balances, pressure-flow relationships, velocity affects, and process control and instrumentation. This detail must be balanced to yield an effective yet tractable model. The power plant model described in this paper contains the necessary process and control parameters required to produce realistic relative component responses. This following describes the basic modeling approach uied in this study.

PC-TRAX Process Model

A PC-TRAX-based process model is a network of pressure and flow nodes. Pressure type nodes calculate the pressure at a specific node based on the flow of material in and out of the nodal volume. Pressure type nodes typically describe large volume components such as a steam condenser or deaerator. Flow type nodes calculate flow at a specific node based on the upstream and downstream pressure. Therefore, under most circumstances, flow nodes must be connected exclusively to pressure nodes and vice versa. Flow nodes usually describe small volume elements such as steam turbine sections or steam

economizers. Figure 2 shows the flow of thermodynamic and hydrodynamic information between nodes.

DIRECTION OF FLOW ’ P P -

W W W H* PRESSURE f H’

X’

FLOW NODE

H X’ NODE X’

Figure 2 : PC-TRAX Hydrodynamiflhermodynamic Information Flow Scheme

The left hand side of Figure 3 shows a simple illustration of a HRSG component typically found in combined cycle power plants. In the HRSG, high temperature flue gas is cooled through the raising and superheating of steam. Shown in the drawing are heat transfer surface for an economizer, control vdve, evaporative steam drum, and superheater. ,: The ’ ’

right hand side of Figure 3 contains a block diagram of the appropriate TRAX &hules required to generate a dynamic model that duplicates the HRSG configuration. The appropriate hydrodynamic and thermodynamic information passes between modules by interconnecting flowstreams according to the scheme shown in Figure 2.

Flue G a to Sack

b

Steam

BFW Pump

Figure 3 : HRSG Schematic and Block Flow Diagram of TRAX HRSG Model

ACSL Process Model

Near term process equipment such as the carbonizer and PFBC were coded in ACSL and dynamically interfaced with the standard TRAX-based process model. The individual process components modeled in ACSL use the same pressure-flow relationship described above. However, the modules are oRen much more complex due to the presence of reducing chemistry and solids-gas hydrodynamics not found in the typical TRAX module. A summary description of some of the custom ACSL models is given below.

Carbonizer/PFBC: Both the carbonizer and PFBC are pressure nodes. Each model accounts for both reducing and oxidizing gaskolids chemistry. Solid-gas hydrodynamics are accounted for as well as variable solids particle size distribution. Pressure drop is calculated based on the superficial gas velocity and an differential energy balance determines average vessel temperature and thermal loss to ambient. A differential equation describes thermal storage in the refiactory of the pressure vessel. A pressure differential determines the average vessel exit pressure.

FBHE: The FBHE, a pressure type node, consists of seven individual fluidized cells, six of which contain heat transfer surface area. Heat transfer surface area comes in the form of submerged tube bundles, submerged enclosure wall surface, and exposed enclosure wall surface. Convection is the predominant mode of heat transfer for the submerged surface while radiation is the predominant mode for the exposed surface. It i$ assumed that there are no solid-gas reactions in the FBHE. .Temperature differentials describe the bulk solids- gas temperature of each cell. Pressure drop and absolute pressure are determinations are identical to those of the carbonizer/PFEiC.

Cvclones/Candle Filter Models: Both components are pressure type nodes. The piping : that separates the components are flow type nodes. The cyclone assumes c9 stant separation efficiency and calculates pressure drop based on the flow rate of gas through the component. The candle filter pressure drop depends on gas flow and cake thickness upon the filter elements. Cake thickness depends primarily on solids loading as well as trigger pressure set point. Differential equations determine the bulk exit temperature and pressure and heat loss to ambient for both vessels.

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Topping Combustor Model: The topping combustor, a flow node, was modeled in some of the system configurations described within this paper. The topping combustor model accounted for both oxidizing and reducing conditions. Differential equations determine the bulk exit temperature and pressure and heat loss to ambient A differential equation determines metal thermal storage losses.

Ash Cooler Model: The ash cooler model is a flow type node and utilizes the NTU- effectiveness method to determine solids and water outlet temperatures. It is assumed that there is no energy or material storage. Water flow through the aih coolers is based on pressure differences between inlet and outlet.

PC-TRAX Control Model

Process control loops were identified based on process constraints. Individual loop types, or configurations, were based on past experience with conventional power generating system controls. A Scientific Apparatus Manufacturers Association (SAMA) diagram was developed for each control loop. TRAX-based process control models were then developed by linking the appropriate T W modules to obtain the desired configuration. All process control and instrumentation model components utilize standard PC/TRAX

modules. The standard TRAX module library supports a full compliment of SAMA based control elements. Module types that were used in this study include: signal transmitters, various mathematical operators, finetion generators, three mode controllers (PID), three element controllers, auto-manual stations, and lead-lag elements.

The left hand side of Figure 4 shows a typical SAMA diagram of a PID controller used to maintain steam turbine header pressure. The configuration consists of a pressure transmitter, error generator, PID controller element with limit switch, an auto manual station with set point signal tie back, and a control valve. The right hand side of Figure 4 shows the appropriate TRAX blocks required to emulate the PID controller configuration. As shown in the figure, there is an almost one to one correspondence between the SAMA diagram and the TRAX module configuration.

PID Controller with Limit Switch

Au to/Manual Station

Figure 4 : SAMA

> < PID Controller

I AIM

Control Valve

and TRAX Model Block Diagram of Header Pressure Controller

Following completion of the process model, individual process..control models were developed for each of the process control loops and integrated with the process model. The controllers were placed in automatic mode and tuned on-line to determine the appropriate proportional, integral, and derivative gains for the controller. The on-line tuning procedure consisted of initiating set point changes or process upsets followed by observation of the specific control variable response. Controller gains were then tuned to generate the desired control variable response within rate and stability constraints. Figure 5 shows a typical controller and process variable response generated during an on-line tuning procedure.

I CONTROLLER RESPONSE 1

1510 I 85

80

g 75

70

i? ;; 55

5 50

4 45 -I

40

35 30 I I I I 1 1460

0 5 10 15 20 25 30

T I E (ninutes)

I

Figure 5 : Typically Controller Response Following On-line Tuning

MODEL RESULTS AND ANALYSIS

Initial model analysis centered around an examination of a commercial sized APFBC power plant. The master control scheme used in this application was such that total plant power output was controlled by fresh coal flow to the carbonizer. Additionally, process air header control is designed to maintain a low he1 to air ratio in the PFBC vessel. This approach is referred to as the maximum efficiency approach and attempts to preserve high cycle efficiency even during plant turndown. Significant interaction between the PFBC/FBHE and steam bottoming cycle adversely affected plant stability following any plant load changes. The transient results generated were unfavorable but helpfbl in understanding some basic concepts. A short discussion of this work follows. This is followed by a discussion of a follow up study that built upon the lessons learned from the APFBC study.

APFBC Application

Figure 6 shows a plot of carbonizer coal flow, carbonizer temperature, and carbonizer pressure for a 10 percent decrease in coal flow at a rate of 1 percent a minute. During the ramping period, carbonizer temperature is maintained at the set point value of 1,600 OF,

and the pressure slowly starts to decrease. The decrease in carbonizer pressure is

expected and reflects a decrease in gas flow through the carbonizer. Approximately ten minutes after the completion of the coal flow ramp, carbonizer temperature and pressure both become unstable.

TCARB 1650. -

1630. -

1610. -

1590. -

1570. -

WZCOAL XAWB 10 Aug 94 1.600 - 210.0

1.540 - 198.0 -

1.480 - 186.0 -

IC

1.420 - 174.0 -

1.360 - 162.0 ,

1550. '* 1.300 150.0 30000 1 1 , 30600 31200 31800 32400 33000 *3

T h e , Seconds X

E5

Figure 6 : Carbonizer Variables for 10% Decrease in Coal at l%/min

Figure 7 shows a plot of carbonizer coal flow, bulk PFBC temperature, and solids flow through the reheater pass of the FBHE for the transient described above. During the coal ramp period, the PFBC temperature is remains stable but wanders about 8 OF from the 1,600 OF set point. The initial dip in PFBC temperature is caused by a decrease in the char flow which closely follows the coal ramp. As the air flow to--the PFBC decreases in response to a change in the fbeVair ratio (air is bypassed to the gas turbine combustor), the PFBC temperature rises back to 1,600 OF. Following this, the PFBC temperature experiences several large temperature excursions.

Attempts to maintain a high he1 to air ratio in the PFBC while controlling PFBC temperature were unsuccessfbl. The quick dynamics of the process air bypass and gas turbine formed a tug of war with the temperature control and heat removal considerations in the FBHE. This is evident in Figure 8: the nadir of the air valve bypass position corresponds to the apex of the steam turbine throttle flow. Maximum and minimum values of steam turbine throttle flow corresponds to the same of the PFBC temperature shown in Figure 7. Increased PFBC temperature, which leads to excessive steaming in the FBHE, corresponds with maximum throttle flow values.

TCOMB 1650. .

1630.

WZCOAI . 6 O O

1610.

1590.

1570.

1550. X

.540

L .480

L.420

1.360

1.300 0

fB2MDLZ WSSR 1.000

1.600

1.200

0.800

0.400

10 Aug 94

FBliE SOLIDS FLOU (WSSR)

IO 30600 31200 31100 32400 33000 E5 E6 Time, Second8

I'

Figure 7 : PFBC/FBHE Variables for 10% Decrease in Coal at l%/mid

48.00

36.00

24.00

12.00

'0.00 x

1.540 ~ 1.520

1.480 - 1.440

1.420 - 1.360

1.360 - 1.280

1.300 1.200 n a 31 E5 86

10 Aug 94

Figure 8 : Process Variables for 10% Decrease in Coal at l%o/min

Gas turbines typically have relatively rapid dynamics as compared to large volume components such as the PFBC or FBHE. These quick gas dynamics can be easily influenced by the additiodsubtraction of cold bypass air. Large pressure fluctuations in the gas turbine combustor/expander assemblage, caused by either flow or temperature affects, can cascade backward thus affecting the PFBC. The PFBC and FBHE are large volume vessels (the freeboard volume of the PFBC is several orders of magnitude greater than that of the gas turbine) with significant thermal inertia generated by the pinwheel, or circuit, of circulating solid material. The dynamics of the PFBC/FBHE circuit, heavily influenced by the large thermal inertia and relatively large gas volume, are much slower than the rapid dynamics of the gas turbine. More importantly, the PFBCRBHE circuit dynamics are much slower than those of the ( S / T ) bottoming cycle which directly affects PFBC/l?FJHE circuit pexformance through heat recovery in the FBHE. Heat removal in the FBHE has a significant affect on the PFBC operating temperature. Additionally, because the HRSG and FBHE both have steam drums, heat removal in the HRSG drum can also have an affect on heat removal in the FBHE superheat circuitry due to either system starving or excessive steaming. To obtain adequate plant response, the master control , scheme utilized in the APFBC study would have to be modified. The coupling impo,s 'd by the maximum efficiency approach would have to be mitigated.

I

! :B 1 - 112 Generation PFBC Atylication

A follow-up effort examined a commercial sized 1-1/2 Generation PFBC combined cycle. The 1-1/2 Generation PFBC combined cycle replaces low-Btu fuel gas generation in the carbonizer with a stream of pressurized natural gas. Many of the lessons learned in the initial effort were applied to model and master control scheme development. The overall control approach utilized in this study did not attempt to maintain a high he1 to air ratio in the PFBC vessel. Instead, a variable fuel air ratio was used to maintain PFBC vessel temperature.

Figure 9 shows a plot of the model predicted power output levels for total power, steam turbine power, and gas turbine power output for a turndown in plant load from design levels to 60 percent of design load. Turndown corresponds to a 28 percent decrease in natural gas flow at a five percent per minute rate. As shown, following a smooth turndown, the plant operates at the new 60 percent condition and is then turned up to the original design load condition.

Figure 10 shows 0, and CO, concentrations in the PFBC flue gas during the transient shown in Figure 9. Following plant turndown, 0, levels increase and CO, levels decrease due to decreased coal flow rate to the PFBC initiated by the control system during turndown. Although not shown, bulk PFBC vessel temperature was maintained at the desired set point value. Also shown in the figure is the flue gas flow exiting the PFBC. As expected, the flow rate decreases during the turndown and is restored to the design condition following plant turn-up to design load.

14.0

1 20

20

POWER OUTPUT -TURNDOWN TO 60%0F DESIGN LOAD ( Natural Gas Decreased 28% @ 5%/mn ) I

t TOTAL POWER

OIT POWER

I- I 01 I I I I I I I I I I

I

0 10 20 30 40 50 60 70 80 90 100 110 I20 [ Bamer Filter Delta-P Variable 1 TlME (ninutes)

I '

Figure 9 : Power Output for Turndown to 60 Percent of Design Load

I

I FLUE GAS -TURNDOWN TO 60% OF DESIGN LOAD I 0.2 , 1500

0.1 8

0.1 6

0.1 4 (I) z 0 0.12 5 $ 0.1 LL

2 0.08 ' 0.06 I 0.04

c02

I

1400

1 'loo

I l l l l l l l l l l l l I l l t l l l t l l 0 1000 0 10 20 30 40 50 60 70 80 90 100 110 120

TlME (minutes)

Figure 10 : Flue Gas Composition for Turndown to 60 Percent of Design Load

I

Control Approaches

The control approach used in generating the transient shown in Figure 9 was "steam- turbine following". This approach requires that plant load changes be initiated by the gas turbine, with the steam turbine controller "following" the change to a new power output. The primary control for changing the steam turbine load involves manipulating heat transfer surface or solids distribution in the FBHE, although the amount of steam generated in the HRSG can also be controlled by dampers andor flue gas bypass arrangement.

The controllers can also be configured into a "coordinated" approach. In this case, plant load changes are initiated by the gas and steam turbine simultaneousb. Another possible control approach is "gas-turbine following". In this approach, plant load changes are initiated by the steam turbine with the gas turbine controller "following" the transient. Figure 11 contains a plot for total plant power output for a turndown to 60 percent of design load for each of these three controller configurations. As can be seen in the figure, a final power output level is attained faster with "gas-turbine following".

COORDINATED

10 15 20 25 30 35 40 TIME (minutes)

Bamer Filter Delta-P Variable

Figure 11 : Power Output for 60 YO Turndown for Three Control Approaches

First Generation Operation

A characteristic of the power cycle investigated in this report is that, in a broad sense, the gas turbine and steam turbine each have separate fbel sources. Thermal input provided by natural gas flow is primarily utilized and converted to electrical energy by the G/T. However, a significant portion of this energy is rejected and recovered by the S / T . The amount of natural gas thermal input recovered and utilized by the S / T is relatively minor when compared to the energy provided to the S / T by coal flow. Thermal energy input provided by the coal feed is mainly used by the S/T, even though a relatively small portion is utilized in the G/T. Recognizing the relative relationships of the G/T and S / T and their corresponding principal source of thermal input, it is possible to formulate a generaliid concept in which the G/T and S / T are operated and/or controlled in a quasi-independent manner.

Figure 12 illustrates an example of how this concept works. The initial transient at the twenty minute mark results from a decrease in natural gas flow from design level to zero at S%/min. The FBHE heat removal rate is kept at near design conditions. In this mode, the plant is running as a first generation plant at the 64 percent of design load level. After . 30 minutes at the steady-state 64 percent of design load condition, a second transie initiated at the sixty-five minute mark. The second transient decreases power ou . t by redistributing solids flow in the FBHE. Plant turndown is effectively independent of the gas turbine, which maintains a near constant power output following the initial plant turndown.

%""

I POWER OUTPUT -TURNDOWN TO 50% OF DESIGN LOAD 1

140

120 - z loo Y 2 80

0 60

2 40

20

5 5

SIT POWER

GIT POWER

0 10 20 30 40 50 60 70 80 90 100 TIME (minutes)

Figure 12 : Power Output for Individual Cycle Turndown

CURRENT WORK

Recent analysis by DOE has shown the potential for improved plant operability and increased plant output for Advanced PFBC plants coupled with an external motor-driven boost compressor.[2] This compressor increases main system pressure such that the gas turbine expander operates at the design expansion ratio and allows for more efficient use of the gas turbine. A dynamic model of this concept is currently under development and analysis.

ACKNOWLEDGMENT

Much of the original process model described in this paper was conceived and developed by Mark Torpey of Foster Wheeler Development Corporation. The work described in this paper was performed for METC under DOE contract DE-AM21-94MC31166. The METC project manager is Donald Bonk. .

REFERENCES

1. Commercial Second-Generation PFBC Plant Transient Model. Final Report, v p o r t No. 9514. Contract No. DE-AC21-89MC25177, Task 15, April 1995.

2. Effects of External Boost Comt>ression on Gas Turbine Performance in CPFBC Applications, M.D. Freier, H.N. Goldstein, and J.S. White, "Thirteenth Annual International Pittsburgh Coal Conference", September, 1996.