Dynamic Modeling and Simulation of a Palm

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    Renewable Energy 28 (2003) 12351256

    www.elsevier.com/locate/renene

    Dynamic modeling and simulation of a palmwastes boiler

    T.M.I. Mahlia a,, M.Z. Abdulmuin b, T.M.I. Alamsyah c,

    D. Mukhlishiend

    a University of Malaya, Department of Mechanical Engineering, Kuala Lumpur 50603, Malaysiab Open University of Malaysia, Centre for Engineering and Technical Studies, Block A, Level 4,

    Academy of Islamic Studies Buildings, Universiti Malaya, Kuala Lumpur 50603, Malaysiac University of Syiah Kuala, Department of Mechanical Engineering, Darussalam 23111, Banda Aceh,

    Indonesiad University of Syiah Kuala, Department of Chemical Engineering, Darussalam 23111, Banda Aceh,

    Indonesia

    Received 27 March 2002; accepted 3 October 2002

    Abstract

    A state-space dynamic model for a palm wastes boiler is being developed and simulated.The unique feature of this boiler is that it uses wastes in the form of fiber and shell from thepalm oil processing as its fuels. Specific characteristics of oil palm waste boilers are non-uniform fuel feed, compositions, sizes and moisture content of the fuel. These features intro-duce additional dimensions to the difficulty of boiler control. The superheated steam producedis used to generate electricity, which drives numerous motors and other equipment for palmfruit processing thus causing severe interactions between the power plant and other parts ofthe mill. The main work of this paper is the development of a dynamic model and simulation

    of the boiler. The boiler unit can be divided into several sections for analysis viz., the furnace,superheater, drum, risers, and downcomer. A tenth-order, physical, linearized process modelwas developed. The linearized model consists of ten first-order simultaneous equations and isrepresented by a (10 x 10) state matrix and (4 x 10) input matrix in the state space form. 2002 Elsevier Science Ltd. All rights reserved.

    Keywords: Palm wastes boiler; Dynamic modeling; State space; Simulation; Power plant

    Corresponding author. Tel.: +603-7967-6842; fax: +603-7967-5317. E-mail address: [email protected] (T.M.I. Mahlia).

    0960-1481/03/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved.doi:10.1016/S0960-1481(02)00218-5

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    Nomenclature

    Aw, As, Ar, Ad steam drum surface, superheater, riser, and downcomer flowareas (m2, ft2)

    A, B, C, D matrices of constant coefficients of the systemCp, Cg, Cst, Crt heat capacitance of superheated steam, flue gas, superheater,

    and riser tubes (J/kg C, Btu/lb F)Dr, Ds, Dd riser, superheater, and downcomer tube diameters (m, ft)

    fs, fr, fd superheater, riser, and downcomer friction coefficientshi, hw, hv, hr, hs, hf enthalpy of liquid, saturated liquid, vapor, liquidvapor

    mixture, and superheated (J/kg, Btu/lb)

    kec drum liquid mass evaporation rate constant (kg/s C, lb/s F )

    kF gas temperature/fuel rate constant (C s/kg, F s/lb)ks, kr, kgs, kgr heat transfer coefficients for superheater and riser tubes to

    steam and boiling liquid and from flue gas to superheater and risertubes (J/kg C, Btu/lb F)

    Ls, Lr, Ld superheater, riser, and downcomer tube lengths (m, ft)

    Ms,Mr, Mw superheater tubes, riser tubes, and steam drum liquid mass (kg,

    lb)

    ps, pv, pw superheater, steam, and water-drum pressures (bar, psig)

    Qg,Qgs,Qs,Qgr,Qr,Qf steady-state heat release and heat input rates from fluegas and calorific value (J/s Btu/s)

    Tg, Tgs, Tgr flue gas temperatures (C, F)Ts, Tv, Tw superheated steam, saturation, and liquid temperatures (C, F)Tst, Trt superheater and riser tube-wall temperatures (C, F)Vw, Vv liquid and vapor-phase volume of steam drum (m

    3, ft3)

    wA/wF air/fuel ratio

    ws, wv, wr, wd, we, wi, wF, wec mass flows of steam or water at superheater,riser, downcomers, feed water, fuel, and drum liquid evaporation

    (kg/s, lb/s)

    x riser outlet mixture quality (%)

    x(t) state variable vector of process system

    y water-level displacement (m, ft)

    y(t) system input or control vector [ws, wi, wf, Te]

    rs, rv, rr, rw steam, saturated vapor, liquidvapor mixture and liquiddensities (kg/m3, lb/ft3)

    1. Introduction

    Electricity is now viewed as a necessity. The basic principle functions of powergeneration are to convert energy from any kind of resource to electrical energy and

    to transmit this energy to the consumers. Steam boilers today range in size from

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    those required to heat a small-size home to the very large ones used in electric power

    generating stations. The fundamental requirement for the power plant system is how

    to ensure the smooth and continuous energy flow. To satisfy this requirement, it is

    desirable that the power generation units be properly controlled so that the productionand consumption of energy can be maintained in equilibrium at all times. To reach

    this requirement, many ways of modeling and controls have been applied. Simulation

    of the operation of the system is achieved by the utilization of computers. Modeling

    and simulation provides key information as to the characteristics that are vital for

    the investigation and prediction of the plant. It enables the modeler to measure theperformance of existing or proposed systems under different operating schemes.

    The model developed in this research is intended for further research to understand

    the behavior of palm wastes boilers under steady state and transient operations, and

    can be used in control system and operational optimization studies. This boiler uses

    a different type of fuel from conventional boilers, using fiber and shell waste productsfrom oil palm processing. It has commonly been taken for granted that this energy

    is free in the palm oil mills industry. Specific characteristics of the boiler are non-uniform fuel feed and moisture content in fiber and shell. These features result inadditional dimensions to the difficulty of controlling palm waste boilers. The natureof fuels, stoichiometric air-to-fuel ratio, and mass balance of a palm waste boiler

    are discussed in Ref. [1].

    2. Plant description

    Parameters of the model equations are either computed using construction data or

    identified using the steady state operation test data. Since a large number of variablesare required to describe the boiler system, it is necessary to devise a systematic

    convention for naming the variables. The boiler is modeled based on the follow-

    ing subsystems:

    Furnace,

    Superheater,

    Drum,

    Downcomer,

    Risers.

    The simplified block diagram of oil palm wastes boiler process is presented inFig. 1.

    For simulation purposes, two types of data are required. First, data that will not

    change while the plant is operating physical data. Second, data that will experi-ence small changes when the plant is operating steady state operating data. Thereare many data needed to simulate the systems, and they are obtained by several

    methods given below:

    On-line reading from the boiler plant,

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    Fig. 1. Simplified block diagram of oil palm wastes boiler.

    Design specifications of the boiler, Published work on oil palm waste boiler,

    Calculations from available data,

    Polynomial Curve Fitting (PLCF).

    2.1. Physical data

    Complete physical data of the boiler that is used for simulation are shown in

    Table 1.

    2.2. Steady state operating data

    The steady state operating data have been collected with on line reading from the

    plant. These data are then used to calculate other necessary data together with dataavailable in the design specification of the boiler and steam tables. Steady stateoperating data that are used for the simulation are shown in Table 2.

    3. Methodology

    The important basic equations used in the analysis and developments of the boiler

    model are the following equations [26]:

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    Table 1

    Physical data of the boiler

    Description Values

    Amount of superheater tubes 65

    Outlet diameter of superheater tubes 0.0381 m

    Tick of superheater tubes 0.003505 m

    Superheater tube lengths 2.6 m

    Amount of riser tubes 560

    Outlet diameter of riser tubes 0.0762 m

    Tick of riser tubes 0.003505 m

    Riser tube lengths 4.5 m

    Amount of downcomer tubes 24

    Outlet diameter of downcomer tubes 0.1016 m

    Tick of downcomer tubes 0.003988 mDowncomer tube lengths 5.25 m

    Drum diameter 1.203 m

    Lengths of drum 5.29 m

    Steel boiler and superheater tubes densities 7850 kg/m3

    Table 2

    Steady-state operating data

    Description Values

    Drum outlet pressure 17.24 Bar

    Superheater outlet pressure 16.41 Bar

    Enthalpy of superheated steam 592 kJ/kg

    Liquid vapor mixture density 558.46 kg/m3

    Air temperature 30 CFlue-gas temperature in the furnace 1575 CFeedwater temperature 60 CSuperheated steam temperature 234 CRiser tubes temperature 206 CSuperheater tubes temperature 242 CFuel mass flow 4.51 kg/s

    Steam mass flow 18.8 kg/s

    Riser friction coefficient 0.0531

    Air:fuel ratio 8.036

    Low heating value of fuel 2373 kJ/kg

    Flow equations: NavierStokes-type equations for one-dimensional non-turbulentflow are used in this study. Viscous friction is neglected so that the velocity profileacross the flow is constant. However, a friction loss term proportional to the squareof velocity is included in the momentum equation. Continuity, momentum, and

    energy conservation equations are applied with certain simplifying assumptionsthat will be mentioned in the following section.

    Heat transfer equations: these are empirical equations used to determine the rate

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    of heat transfer from hot gases to tube banks in turbulent flow, from tube wallto steam and to boiling liquid. The tube wall temperatures are determined by the

    heat capacitance of the walls.

    State equations: these equations are obtained from steam tables at saturated andsuperheated steam for the steady state operating conditions. The relations are

    assumed to be linear for a given range of values of the variables.

    Some fundamental physics laws are reviewed in the time-dependent form, and the

    process model is established using the following fundamental equations:

    3.1. Conservation of mass

    The mass balance equation or conservation of mass is expressed by:d(Vr)

    dt win wout. (1)

    3.2. Conservation of energy

    The conservation of energy is the first law of thermodynamics and can beexpressed in terms of the relationship:

    d(Vrhout)

    dt winhin wouthout Q W. (2)

    3.3. Conservation of momentum

    The law of conservation of momentum is expressed in terms of the following[3]:

    PinPout Ln

    gAn

    d wout

    dt fn

    Ln

    g

    w2out

    rout(An)2Dn

    Lnrout 1

    2g(An)2

    w2out

    rout(3)

    w2out

    rout(An)2g

    w2in

    rin(An)2g.

    3.4. Heat transfer

    The risers and superheater are assumed to receive heat from the flue gas by con-vection only. The heat is assumed to be transferred from the flue gas to the metaland from the metal to the fluid by convection only. The equations used are [7]:

    Gas to metal:

    Qg kg w0.6g (Tg Tm) (4)

    Metal to fluid (one phase flow)

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    Q k w0.8 (Tm T) (5)

    Metal to fluid (two phases flow)

    Q k (Tm T)3 (6)

    3.5. Method for model linearization

    The model of a boiler represented by a large number of non-linear partial differen-

    tial equations. Most of the equations are related to fluid flow and heat transfer involv-ing partial derivatives of time and space. Solutions of a set of these equations are

    very difficult and therefore some simplifying assumptions have to be made. In theanalysis, the boiler is divided into a number of sections and for each lumped para-

    meter section, the steam and gas are assumed to vary only in the axial directions

    and linearly with space. Linearizing the partial differential equations reduces theseequations to ordinary linear differential equations by applying small perturbation and

    difference equation techniques. Suppose an equation of the general form:

    fx,y,z,...,xt,xl

    ,yt

    ,yl

    ,... 0 (7)where

    t

    indicates time derivative andl

    is the derivative with respect to the space

    variable. It is assumed that for small space intervals L, the variables x, y, z,... may

    be written in linear functions of the variable l, so that:

    xl

    x2x1

    L,yl

    y2y1

    L,zl

    z2z1

    L,..., (8)

    where x2,y2,z2,..., and x1,y1,z1,..., denote the value of the variable x, y, z,... at the end

    and at the beginning, respectively, of the space interval L. Even though x1,y1,z1,...,

    x2,y2,z2,..., are no longer functions of l, they are still functions of time .

    x,y,z,...,xt

    ,yt

    ,zt

    ,... are now assumed to be the value of variables at the beginning of

    the space interval, hence Eq. (8) can be written as:

    fx1,y1,z1,..., x1t,x2x1

    L,

    y1

    t,y2y1

    L,

    z1

    t

    z2z1

    L,..., 0. (9)

    Eq. (9) is then perturbed at steady state operating conditions to eliminate the non-

    linearities, giving the following equation:

    fx1

    x1 fy1

    y1 ... fx2

    x2 fy2

    y2 f

    (x1)t

    (x1)t

    ... (10)

    0

    where (x1)t

    , (y1)t

    , .... can be replaced byd

    dt(x1),

    d

    dt(y1),... for small pertur-

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    bations. It is seen from the equations above that time-derivative terms

    dx1

    dt,dy1

    dt,dz1

    dt, ... are treated as independent variables and second or higher order terms

    in perturbed variables are neglected. The partial differentials fx1,fy1

    ,fz1

    ,, whichare the coefficients of the perturbed variables, are evaluated at initial steady stateoperating conditions about the dynamic behavior of the boiler to be analyzed. As a

    result of these simplifications, Eq. (10) becomes linear first order ordinary differentialequations with constant coefficients in the perturbed variables written asx1, x2, y1, y2, z1, z2.

    4. Model development

    4.1. General assumptions and abbreviations

    The following general assumptions are made in deriving the dynamic model for

    the boiler. Additional assumptions are listed under each section:

    Feed water temperature is assumed to be constant. State equations for vapor phase are determined from steam tables and estimation

    of the actual pressure, temperature, and density relation within a given range of

    value of the variables.

    Linear relations between the mentioned variables are obtained from steam tables

    both for saturated and superheated steam.

    No rate of change of stored mass in the gas path.

    Turbulent heat transfer rates from hot gas to tube banks or from the superheater

    tube to the steam are obtained from empirical relations.

    The heat transfer coefficients are determined from the steady state operating con-

    dition. A lumped parameter approach with ordinary differential equations is used to

    describe the system.

    Water and steam in the drum and in the risers are in saturation equilibrium.

    Mixture of fiber and shell in the fuel is constant. No mass and momentum transfer at the tube side.

    The following abbreviations are used in the model development:

    COM: Conservation of Mass COT: Conservation of Momentum

    COE: Conservation of Energy

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    4.2. Model development

    4.2.1. Furnace

    The following assumptions are made in deriving the dynamic model for the fur-

    nace:

    The fuel (fiber and shell) consumption is assumed to be constant. Calorific value and moisture content of the mixture of palm fiber and shell are con-

    stant.

    The airfuel ratio is assumed to be constant. Temperature of combustion gases in furnace is proportional to the fuel rate.

    In each tube bank the heat transfer rate is determined by the tube wall temperature,

    the average gas temperature is a function of the temperature of incoming gasesand the amount of the heat loss of that particular bank.

    Inertia of the hot gases is neglected and the velocity changes take place instan-

    taneously.

    Delay due to the heat capacitance of the hot gases is neglected; that is, temperature

    changes take place instantaneously in combustion gases.

    Turbulent heat transfer is assumed throughout the process.

    COM:

    VF d rFdt

    VAdrAdt

    (wF wA) wg (11)

    from point 3 of the general assumptions, it is known that VFd rF

    dt 0,

    VAd rA

    dt 0, therefore (wF wA) wg where Airfuel ratio

    wA

    wF, wA

    wA

    wFwF, wg wF

    wA

    wFwF

    wg 1 wA

    wF wF (12)COT:Not relevant.

    COE:

    Vgd(rghg)

    dt (wFhF wAhA) wghg Qg (13)

    where Vgd(rghg)

    dt 0, wg 1 wA

    wF wF , hg hF hA, therefore

    Qg wg hg, Qg wg Cg Tg

    Qg wg . LHV (14)

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    Tg Qg

    Cg (1 wA/ wF) wF(15)

    4.2.2. Superheater

    The following assumptions are made in deriving the dynamic model for the super-

    heater:

    Inertia term in the flow equation is neglected. Load disturbance is a change in the steam flow rate. To calculate superheater section average gas temperature, both risers are con-

    sidered as one lumped section.

    Gas side

    COM:

    Vgsdrgs

    dt wg wgs (16)

    where Vgsdrgs

    dt 0 therefore

    wg wgs. (17)

    COT:Not relevant.

    COE:

    Vgsd(rgs hgs)

    dt wghg wgshgs Qgs (18)

    where Vgsd(rgshgs)

    dt 0 therefore wghg wgshgs Qgs 0, Qgs

    wghg wgshgs , Qgs wg Cg Tg wgs Cgs Tgs where wg wgs , Cg

    Cgs then Qgs wg Cg (Tg Tgs), Qgs Cg (1 wA/ wF) wF (Tg Tgs)

    Therefore the flue gas temperature leaving superheater banks and entering riserbanks is as follows:

    Tg1 Tg Qgs

    Cg (1 wA/ wF) wF(19)

    Tube Bank

    COE:

    Ms Cstd Tst

    dt Qgs Qs (20)

    where

    Qgs kgs w0.6F (Tgs Tst) (21)

    Tgs Tg 1

    2

    Qgs

    Cg (1 wA/ wF) . wF(22)

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    Qs ks w0.8v (Tst Ts). (23)

    Water/Steam Side

    COM:

    As Lsdrs

    dt ws wv. (24)

    COT:

    pvps fsw2v

    rv. (25)

    COE:

    As Ls drs hsdt

    wv hv ws hs Qs. (26)

    4.2.3. Riser

    The following assumptions are made in deriving the dynamic model for the risers:

    Only natural circulation exists.

    Vapor and liquid velocities in the risers are identical.

    Heat transfer rate to boiling liquid from tube wall is proportional to the cube ofthe temperature difference between the wall and the liquid.

    Liquid temperature is always the same as the saturation temperature correspondingto the drum pressure; that is, instantaneous evaporation takes place in the riser

    when the drum pressure changes.

    Both risers are considered as one lumped section.

    Gas side

    COM:

    Vgrdrgr

    dt wgs wgr (27)

    where Vgrdrgr

    dt 0 therefore wgs wgr.

    COT:Not relevant.

    COE:

    Vgrd(rgr hgr)

    dt wgshgs wgrhgr Qgr (28)

    where Vgrd(rgrhgr)

    dt 0 therefore wgshgs wgrhgr Qgr 0, Qgr

    wgshgs wgrhgr , Qgr wgs Cgs Tgs wgr Cgr Tgr where, wgs wgr ,Cgs Cgr then Qgr wg Cg (Tg Tgr), Qgr Cg (1

    wA/ wF) wF (Tg Tgr).

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    Therefore the flue gas temperature leaving the riser is as follows:

    Tg2 Tg Qgr

    Cg (1 wA/ wF) wF. (29)

    Tube BankCOE:

    Mr Crtd Trt

    dt Qgr Qr (30)

    where

    Qgr kgr w0.6F (Tgr Trt). (31)

    Rewriting Eq. (9); Tg1 Tg Qgs

    Cg (1 wA/ wF) wFtherefore,

    Tgr Tg1 1

    2

    Qgr

    Cg (1 wA/ wF) wF. (32)

    Substituting Eq. (9) into Eq. (32) results in the following equation:

    Tgr Tg Qgs

    Cg (1 wA/ wF) wF

    1

    2

    Qgr

    Cg (1 wA/ wF) wF(33)

    Qr kr (Trt Tv)3. (34)

    Water/Steam side

    COM:

    Ar Lrdrr

    dt wd wr. (35)

    COT:

    pwpv Lr

    gAr

    dwr

    dt fr

    Lr

    g

    w2r

    rrA2rDr

    Lrrr w2r

    2g rrA2r

    w2rrrA

    2rg

    w2d

    rwA2g (36)

    COE:

    ArLrd(rr hr)dt

    wdhw wrhr Qr (37)

    1

    rr

    x

    rv

    (1 x)

    rw(38)

    hr xhv (1x) hw (39)

    hr xhfg hw. (40)

    4.2.4. Drum

    The following assumptions are made in deriving the dynamic model for the drum:

    There is no temperature gradient in the vapor phase in the drum and the tempera-

    ture is always the saturation temperature corresponding to the drum pressure.

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    The liquid phase has no temperature gradient except through a very thin layer at

    the liquid surface because of the turbulence in the drum.

    Evaporation or condensation rate in the drum is proportional to the difference of

    liquid and saturation temperatures. Liquid level changes due to bubble formation in the drum are neglected.

    Feed water temperature is assumed to be constant.

    Gas side

    Not relevant.

    Tube bank

    Not relevant.

    Water/Steam side

    COM:Water

    d

    dt(Vwrw) wi (1 x) wr wd wec. (41)

    Steam

    d

    dt(Vvrv) wec x wr wv (42)

    y Vv

    Aw

    Vw

    Aw(43)

    M Aw rw y. (44)

    COT:

    Not relevant.COE:

    d

    dt

    (Vwrwhw) (1 x) wrhv wihi wdhwwechv. (45)

    4.2.5. Downcomers

    The following assumptions are made in deriving the dynamic model for downco-mers:

    Only natural circulation exists.

    No boiling takes place in downcomers.

    Downcomers liquid temperature is the same as the drum liquid temperature.

    Gas SideNot relevant.

    Tube bank

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    conditions, which is between 17.2 bar (250 psig) and 22 bar (320 psig) of drum

    pressure. The dynamic physical model can be summarized as follows:

    Type of model: state space

    Number of input variables: four

    Steam flow-rate (ws) Feed water flow rate(wi) Fuel flow rate (wF) Feed water temperature flow rate (Ti)

    Number of output variables: ten

    Superheated steam density (s) Superheated steam temperature (Ts) Superheater tube wall temperatures (Tst)

    Quality of mixture leaving riser (x)

    Riser mass flow rate (wr) Drum pressure (Pv)

    Riser tubes wall temperatures (Trt)

    Drum and downcomers liquid temperature (Tw)

    Drum liquid level (y)

    Superheater pressure (Ps)

    The main difficulty in this work is the size and complexity of the boiler unit.When the model was formulated and linearized it was found that many manipulationsteps were required before arriving at the final form of the model. The reason wasthat a set of ten simultaneous differential equations together with large number of

    the steady-state ones needed to be suitably rearranged and solved.

    In simulation, the set of equations developed and linearized in the previous section

    are reduced and rearranged in order to obtain a suitable model for simulation in

    state-space form. This palm wastes boiler model has been simulated using MATLAB.Before the simulation can be performed it is necessary that all the unknown constants

    and parameters are made available to the model. These unknowns include steady-state balance equations and operating points, boiler physical data, and curve fittingrelationship if data extracted from the steam tables. The set of linearized equations

    may be written in the following matrix form:

    x(t) Ax(t) Bu(t) (52)

    y(t) Cx(t) Du(t) (53)

    where A is a (10 x 10) state matrix, B (10 x 4) input matrix, C output matrix and

    direct transmission matrix D are constant matrices. The value of the matrices is

    presented in Appendix A.The response of the output variables for 10% step inputs of steam, feed water,

    flow rate, temperature, and fuel are shown in Figs. 25.

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    Fig. 2. Response with 10% steam flow rate step.

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    Fig. 3. Response with 10% feedwater flow rate step.

    Validation of the model was done by on-line reading of drum pressure from the

    plant using HP 3497A Data Acquisition and Control Unit and HP BASIC as the

    programming language. This data was transferred to a MATLAB file. Pneumaticcylinders were used as mechanisms (actuators) for adjusting the amount of the input

    fuel (fiber and shell) to the furnace of the boiler plant. The responses model for

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    Fig. 4. Response with 10% fuel flow rate step.

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    Fig. 5. Response with 10% feedwater temperature step.

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    drum pressure (Pv) with respect to fuel flow rate (wF) is presented in Fig. 6. Fromvalidation it can be seen that the result obtained is quite encouraging and the simu-

    lated model of drum pressure matches fairly well with the experimental plot.

    6. Conclusion

    In the reduction of the system order, it is important to select dependent variables

    to give the best reduced system. For control studies, it is suggested that the dependentvariables can be reduced to several significant output variables such as:

    superheated steam temperature (Ts)

    quality of mixture leaving riser (x)

    drum pressure (Pv)

    drum liquid level (y)

    superheater pressure (Ps)

    with system inputs:

    feed water flow rate(wi) fuel flow rate (wF) feed water temperature flow rate (Ti)

    and consider the steam flow rate (ws) as a disturbance. In a more simplified structurethe output variables can be reduced to Pv and y only while the input variables arereduced to only one, i.e., wF.

    The model has been developed with certain assumptions that might make the

    model less accurate. The number of assumptions can be reduced especially in the

    riser part, where a more accurate representation can be expected if the riser could

    be derived separately. However, from the validation shown, the result matches fairlywell with the experimental plot. Finally, this model should be useful as a basis for

    further studies of the two following purposes:

    To be a basis for a linearized model to be used for design of a multivariablecontrol system of a palm wastes boiler.

    Fig. 6. Steam drum pressure response with 20% fuel flow rate step.

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    To be a basis for a reduced order linearized transfer function model for related

    control applications.

    Acknowledgements

    The authors would like to acknowledge the financial support from the Ministryof Science, under the IRPA financing scheme. The research was carried out underIRPA research Project No. 03-02-03-0353.

    Appendix A

    Rewriting Eq. (25), pvps fsw2v

    rv or in perturbed form can be written as:

    pvps fs2 wv

    rvpv fs

    w2v

    r2v rv wv

    rv

    fs 2 wvpv

    rv

    fs 2 wvps

    wv

    2 rv rv. Then in simplified form, wv z1 pv z2 ps z3 rv

    where z1 rv

    fs 2 wv, z2

    rv

    fs 2 wv, z3

    wv

    2 rv rv.

    Input matrices A (10 x 10) and B (10 x 4) and output matrix C and D:

    A

    0.85972 0.00092 0 0 0

    15.93825 0.22675 0.15181 0 0

    42.04492 0.14517 0.10124 0 0

    0.00441 4.7223 10-6 0 0.17506 3.02126 10-8

    5264.27236 0.96792 2.91963 1.00392 106 0.92565

    1285.64960 1.37760 0 0 0

    0 0 0.00044 0 0

    0 0 0 3.51597 0.00035

    6.80509 0.00729 0 269.36171 4.64881 10-5

    56620.34223 78.22541 10.93006 0 0

    1.33932 10-5 0 0 0 0

    0.00025 0 0 0 0

    0.00066 0 0 0 0

    2.24703 10-7 4.12171 106 0.00013 0 0

    4.31077 1830.09555 157.59312 0 0

    0.55027 209.41783 24.49676 0 0

    0.19445 87.82094 0 0 0

    0.00160 0 0.7277 4 0 0

    0.00031 0.00879 0.19556 0 0

    0.88206 0 0 0 0

    B

    0.00339 0 0 0

    0 0 0 0

    0 0 1.49170 0

    0 1.77767 10-7 0 0

    60.69606 23.94852 530.97106 1.16471

    0 0.05186 0 0

    0 0 22.98759 0

    0 0.02530 0 0.00229

    0 2.17627 10-6 0 0

    228.02653 0 0 0

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    C

    1.000 0 0 0 0 0 0 0 0 0

    0 1.000 0 0 0 0 0 0 0 0

    0 0 1.000 0 0 0 0 0 0 0

    0 0 0 1.000 0 0 0 0 0 0

    0 0 0 0 1.000 0 0 0 0 0

    0 0 0 0 0 1.000 0 0 0 0

    0 0 0 0 0 0 1.000 0 0 0

    0 0 0 0 0 0 0 1.000 0 0

    0 0 0 0 0 0 0 0 1.000 0

    0 0 0 0 0 0 0 0 0 1.000

    D

    0 0 0 0

    0 0 0 0

    0 0 0 0

    0 0 0 0

    0 0 0 0

    0 0 0 0

    0 0 0 00 0 0 0

    0 0 0 0

    0 0 0 0

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