A NEW BENCHMARK FOR PLANTWIDE PROCESS CONTROL

Klafke, N.; Souza Jr., M. B. de; Secchi, A. R.

doi:10.1590/0104-6632.20160334s20150210

N. Klafke

Radix Engineering and Software Development. E-mail: natalia@radixeng.com.br

Chemical Engineering Department, Universidade Federal do Rio de Janeiro, (UFRJ), Rio de Janeiro - RJ, Brazil.

M. B. de Souza Jr.^**E-mail: mbsj@eq.ufrj.br

Chemical Engineering Department, Universidade Federal do Rio de Janeiro, (UFRJ), Rio de Janeiro - RJ, Brazil.

A. R. Secchi

Chemical Engineering Program, COPPE, Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro - RJ, Brazil. E-mail: arge@peq.coppe.ufrj.br

*E-mail: mbsj@eq.ufrj.br

*To whom correspondence should be addressed

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Figure 1
Generic TADP Process.

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Figure 2
Process Flowsheet.

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Figure 3
Variation in composition (a) of the reactants and (b) of the products with the reactor inlet temperature.

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Figure 4
Control structure of Strategy 1.

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Figure 5
Control structure of Strategy 2.

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Figure 6
Reaction section regulatory control under disturbance of 10% in A₉/A₁₀ flow rate. (a) and (c) - variation in separator temperature (V-01_TC. PV) with the manipulation of cooler heat duty (V-01_TC. OP). (b) and (d) - variation in reactor temperature (R-01_TC. PV) with the manipulation of furnace heat duty (R-01_TC. OP). Controlled/manipulated variables (solid/dashed lines).

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Figure 7
Reaction section supervisory control under disturbance of 10% in A₉/A₁₀ flow rate. (a) - variation of ethane concentration in the mixer outlet (V-01_CC. PV) with the manipulation of recycle gas flow rate (V-01_CC.OP) for strategy 1. (b) - variation of xylene concentration in reactor outlet (R-01_CC.PV) with the manipulation of the setpoint of reactor temperature (R-01_CC.OP) for strategy 1; (c) - variation of ethane concentration in the overhead of separator (V-01_CC.PV) with the manipulation of purge flow rate (V-01_CC. OP) for strategy 2. Controlled/manipulated variables (solid/dashed lines).

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Figure 8
Sidestream composition in T-02 with disturbance of 10% in A₉/A₁₀ feed stream flow rate.

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Figure 9
Proposed modification in Strategy 1 control structure of T-02.

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Figure 10
Sidestream composition in T-02 with disturbance of 10% in A₉/A₁₀ flow rate for strategy 3.

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Table 1
Specification of the distillation columns.

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Table 2
Equipment dimensions and specifications.

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Table 3
Typical number of steady-state degrees of freedom for process units, based on Araújo et al. (2007b).

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Table 4
Number of steady-state degrees of freedom analysis.

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Table 5
List of manipulated variables.

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Table 6
Selected candidate controlled variables for the HDA process (excluding levels).

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Table 7
Economic data for the process, based on Araújo et al. (2007b) and ICIS.

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Table 8
Effect of disturbances on optimal values of the selected variables.

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Table 9
Summary of the control loops of Strategy 1.

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Table 10
Summary of the control loops of strategy 2.

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Table 11
Summary of the control loops of Strategy 3.

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An Aromatic hydrocarbon compound with n carbons An+ Cut composed of aromatic hydrocarbons with n carbon atoms of the lighter component An- Cut composed of aromatic hydrocarbons with n carbon atoms of the heavier component Cn Hydrocarbon compound with n carbon atoms Cn+ Cut composed of hydrocarbons with n carbon atoms of the lighter component Cn- Cut composed of hydrocarbons with n carbon atoms of the heavier component c Controlled variable u Manipulated variable d Disturbance variable cs Controlled variable reference value J Objective function Kc Proportional gain τI Integral time constant

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Table A1
Kinetics parameters of the model, based on Ouguan et al. (2007).

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(A1)

(A2)

(A3)

(A4)

(A5)

(A6)

(A7)

(A8)

(A9)

(A10)

(A11)

(A12)

(A13)

(A14)

	Distillation Columns
	T-02	T-03	T-04
Number of stages	35	44	52
Pressure at the top [Pa g]	61.2	6.1	59.1
Feed stage	24	24	24
Sidestream stage	5	7	-
Diameter [m]	3.9	5.8	5.7
Specification 1 (mass basis)	Boilup ratio = 2	Distilled = 10^-11 kg/h	Distilled = 144338 kg/h
Specification 2 (mass basis)	Ratio distilled/feed = 0.018	Boilup ratio = 5.748	Reflux ratio = 1.4
Dimensions of the reflux and reboiler - Diameter x Length (m)
Reflux drum	1.91 x 5.7	3.7 x 11	2.8 x 8.3
Base drum	3.4 x 10	4.6 x 13.9	4 x 12

Reactor	Length	8	m
Reactor	Diameter	5.3	m
FEHE (Feed Effluent Heat Exchanger)	UA	2823.5	kJ/(s°C)
Separator	Length	10	m
Separator	Diameter	3	m

Process Unit	Degrees of Freedom
Each external feed stream	1 (feedrate)
Splitter	n-1 split fractions (n is the number of exit streams)
Mixer	0
Compressor, turbine, and pump	1 (work)
Adiabatic flash tank	0^* * Add 1 degree of freedom if pressure is set (need an extra valve, compressor, or pump).
Liquid phase reactor	1 (holdup)
Gas phase reactor	0^* * Add 1 degree of freedom if pressure is set (need an extra valve, compressor, or pump).
Heat Exchanger	1 (duty or net area)
Columns (e.g. distillation) excluding heat exchangers	0^* * Add 1 degree of freedom if pressure is set (need an extra valve, compressor, or pump). + number of side streams

Process Unit	Degrees of Freedom
External feed streams	4 × 1 = 4
Splitters (purge)	1 × 1 = 1
Compressor(^* * Considering fixed power in the compressor. )	1 × 0 = 0
Adiabatic flash(^ Assuming no adjustable valves for pressure control (fully open valve ahead of the separator). ) (separator)	1 × 0 = 0
Gas phase reactor (^ Assuming no adjustable valves for pressure control (fully open valve ahead of the separator). )	1 × 0 = 0
Heat exchangers in recycle section (^* ***** The FEHE duty is not a degree of freedom because there is no adjustable bypass. ) (furnace and cooler)	2 × 1 = 2
Heat exchangers in three distillation columns	3 × 2 = 6
Three distillation columns, two of it with one sidestream each	0 + 2 × 1 = 2
Total	15

	Manipulated Variable	State
U1	A₉/A₁₀ feed flow rate	Steady State
U2	Fresh gas feed flow rate	Steady-state
U3	Fresh toluene flow rate	Steady-state
U4	Bentol flow rate	Steady-state
U5	Furnace heat duty	Steady-state
U6	Cooler heat duty	Steady-state
U7	Purge flow rate	Steady-state
U8	Liquid flow to stabilizer	Dynamic only (level control)
U9	Stabilizer reflux flow rate	Steady-state
U10	Stabilizer condenser duty	Dynamic only (level control)
U11	Stabilizer distillate flow rate	Steady-state
U12	Stabilizer reboiler duty	Steady-state
U13	Stabilizer bottoms flow rate	Dynamic only (level control)
U14	Benzene column reflux flow rate	Steady-state
U15	Benzene column distillate flow rate	Dynamic only (level control)
U16	Benzene column reboiler duty	Steady-state
U17	Benzene column bottoms flow rate	Dynamic only (level control)
U18	Toluene column reflux flow rate	Steady-state
U19	Toluene column condenser duty	Steady-state
U20	Toluene column distillate flow rate	Dynamic only (level control)
U21	Toluene column reboiler duty	Steady-state
U22	Toluene column bottoms flow rate	Dynamic only (level control)

Y1	A9/A10 flow rate	Y26	Separator liquid outlet toluene mol fraction
Y2	Fresh toluene flow rate	Y27	Separator liquid outlet xylene mol fraction
Y3	Recycle flow rate of toluene	Y28	Gas recycle ethane mol fraction
Y4	Reactor inlet temperature	Y29	Gas recycle propane mol fraction
Y5	Reactor outlet temperature	Y30	Gas recycle benzene mol fraction
Y6	Separator temperature	Y31	Total flow rate of hydrocarbons to the reaction section
Y7	Bentol feed flow rate	Y32	Hydrogen mol fraction in the reactor outlet
Y8	Fresh gas feed flow rate	Y33	Production rate (flow rate in benzene and stabilizer columns)
Y9	FEHE hot side exit	Y34	Production rate (flow rate in the toluene column)
Y10	Steam flow rate at the separator outlet	Y35	Temperature in an intermediate stage of stabilizer column
Y11	Liquid flow rate at the separator outlet	Y36	Temperature in an intermediate stage of benzene column
Y12	Purge flow rate	Y37	Temperature in an intermediate stage of toluene column
Y13	Separator pressure	Y38	Pressure at the top of stabilizer column
Y14	Furnace heat duty	Y39	Pressure at the top of benzene column
Y15	Cooler heat duty	Y40	Pressure at the top of toluene column
Y16	Toluene conversion at reactor outlet	Y41	Benzene mol fraction in stabilizer column sidestream
Y17	Trimethylbenzene conversion at reactor outlet	Y42	Propane mol fraction in stabilizer column sidestream
Y18	Hydrogen / hydrocarbons ratio in the reactor inlet	Y43	Benzene mol fraction in benzene column sidestream
Y19	Recycle gas flow rate	Y44	Benzene mol fraction in benzene column sidestream
Y20	Mixer ethane mol fraction	Y45	Xylene mol fraction in toluene column bottoms
Y21	Mixer propane mol fraction	Y46	Toluene mol fraction in toluene column bottoms
Y22	Separator overhead vapor ethane mol fraction	Y47	Ethylbenzene mol fraction in toluene column bottoms
Y23	Separator overhead vapor propane mol fraction	Y48	Toluene mol fraction in toluene column overhead
Y24	Separator overhead vapor benzene mol fraction	Y49	Xylene mol fraction in benzene column overhead
Y25	Separator liquid outlet benzene mol fraction

Candidate Controlled Variable	Nominal Value	Absolute Variation of Nominal Value with D1	Absolute Variation of Nominal Value with D2
Mixer outlet ethane mol fraction	1.004x10^-6	4.48x10^-7	-4.87x10^-7
Mixer outlet propane mol fraction	5.134x10^-8	2.33x10^-8	-2.59x10^-8
Separator overhead vapor ethane mol fraction	8.54x10^-3	-2.16x10^-4	3.30x10^-4
Separator overhead vapor propane mol fraction	4.37x10^-4	-5.15x10^-6	1.10x10^-5
Separator overhead vapor benzene mol fraction	1.02x10^-4	1.29x10^-5	-1.47x10^-5
Separator liquid outlet benzene mol fraction	0.0702032	0.0030892	-0.0035004
Separator liquid outlet toluene mol fraction	0.254397	-0.0017485	0.0023585
Separator liquid outlet xylene mol fraction	0.200455	-0.0099576	0.0101899
Gas recycle benzene mol fraction	1.20x10^-8	2.33x10^-8	-2.59x10^-8
Reactor outlet xylene mol fraction	0.2004806	9.96x10^-7	1.02x10^-7

Tag	Manipulated variable	Controlled variable	K_c (%/%)	τ_I(min)
R-01_TC	F-01 heat duty	R-01 inlet temperature	17.15	3.96
V-01_TC	PREAC cooler heat duty	V-01 temperature	1	20
V-01_PC	V-01 purge flow rate	V-01 pressure	20	12
V-01_LC	V-01 output flow rate	V-01 level	10	-
V-01_CC	Recycle gas flow rate	M-01 output ethane concentration	1	20
R-01_CC	Reactor temperature	R-01 output xylene concentration	1	20
T02_CondPC	T-02 sidestream flow rate	T-02 pressure	44.19	85.8
T02_DrumLC	T-02 condenser heat duty	T-02 reflux drum level	2	-
T02_CC01	T-02 reflux flow rate	T-02 sidestream toluene concentration	0.42	11.88
T02_TC	T-02 reboiler heat duty	T-02 temperature control tray	26.21	19.8
T02_CC02	T-02 temperature control tray	T-02 bottom benzene concentration	0.11	11
T02_SumpLC	T-02 bottom flow rate	T-02 reboiler level	2	-
T03_CondPC	T-03 condenser heat duty	T-03 pressure	98.99	2.64
T03_DrumLC	T-03 sidestream flow rate	T-03 reflux drum level	2	-
T03_CC01	T-03 reflux flow rate	T-03 sidestream benzene concentration	1	20
T03_TC	T-03 reboiler heat duty	T-03 temperature control tray	57.4	6.6
T03_CC02	T-03 temperature control tray	T-03 bottom benzene concentration	0.21	2.59
T03_SumpLC	T-03 bottom flow rate	T-03 reboiler level	20	-
T04_CondPC	T-04 condenser heat duty	T-04 pressure	52.88	5.28
T04_DrumLC	T-04 distillate flow rate	T-04 reflux drum level	20	-
T04_CC01	T-04 temperature control tray	T-04 distillate xylene concentration	2.16	5.28
T04_TC	T-04 reflux flow rate	T-04 temperature control tray	0.73	4.92
T04_CC02	T-04 reboiler heat duty	T-04 bottom toluene concentration	860.6	2.64
T04_SumpLC	T-04 bottom flow rate	T-04 reboiler level	2	-

Tag	Manipulated variable	Controlled variable	K_c (%/%)	τ_I (min)
R-01_TC	F-01 heat duty	R-01 inlet temperature	17.15	3.96
V-01_TC	PREAC cooler heat duty	V-01 temperature	1	20
V-01_PC	Pure Hydrogen Flow	V-01 pressure	20	12
V-01_LC	V-01 output flow rate	V-01 level	10	-
V-01_CC	V-01 purge flow rate	V-01 ethane concentration in the top output	1	20
T02_CondPC	T-02 sidestream flow rate	T-02 pressure	44.19	85.8
T02_DrumLC	T-02 condenser heat duty	T-02 reflux drum level	2	-
T02_CC01	T-02 temperature control tray	T-02 sidestream toluene concentration	0.42	11.88
T02_TC	T-02 reboiler heat duty	T-02 temperature control tray	44.2	85.8
T02_SumpLC	T-02 bottom flow rate	T-02 reboiler level	2	-
T03_CondPC	T-03 condenser heat duty	T-03 pressure	98.99	2.64
T03_DrumLC	T-03 sidestream flow rate	T-03 reflux drum level	2	-
T03_CC01	T-03 temperature control tray	T-03 sidestream benzene concentration	1	20
T03_TC	T-03 reboiler heat duty	T-03 temperature control tray	57.4	6.6
T03_SumpLC	T-03 bottom flow rate	T-03 reboiler level	20	-
T04_CondPC	T-04 condenser heat duty	T-04 pressure	52.88	5.28
T04_DrumLC	Fresh toluene flow rate	T-04 reflux drum level	20	-
T04_CC01	T-04 temperature control tray	T-04 bottom toluene concentration	0.32	22.44
T04_TC	T-04 bottom flow rate	T-04 temperature control tray	6.12	17.16
T04_SumpLC	T-04 reboiler heat duty	T-04 reboiler level	2	-

Tag	Manipulated variable	Controlled variable	K_c (%/%)	τ_I(min)
T02_CondPC	T-02 sidestream flow rate	T-02 pressure	44.19	85.8
T02_DrumLC	T-02 condenser heat duty	T-02 reflux drum level	2	-
T02_CC03	T-02 fuel gas output flow rate	T-02 side stream propane concentration	0.42	11.88
T02_TC	T-02 reboiler heat duty	T-02 temperature control tray	26.21	19.8
T02_CC02	T-02 temperature control tray	T-02 bottom benzene concentration	0.11	11
T02_SumpLC	T-02 bottom flow rate	T-02 reboiler level	2	-

Reaction	Direct reaction		Reverse reaction
Reaction	k_0i, s^-1	E_ai, kJ mol^-1	k_0i/K, s^-1	*(E_ai)_inv = E_ai* - ΔG, kJ mol^-1**
1	9.106 x 10¹⁰	102	3.269 x 10¹¹	94.8
2	9.534 x 10¹³	150	1.567 x 10¹⁵	134.1
3	5.712 x 10¹⁰	96.77	1.273 x 10¹¹	92.07
4	6.001 x 10¹³	150	2.804 x 10¹⁵	127.8
5	6.126 x 10¹⁰	101.8	-	-
6	3.263 x 10¹⁰	95.8	-	-
7	3.213 x 10⁹	106	1.338 x 10¹¹	84.7

[1] *E-mail: mbsj@eq.ufrj.br

p_B	0.256	$/kg
p_X	0.312	$/kg
p_Tol	0.145	$/kg
P_A _9A10	0.072	$/kg
p_H ₂	1.455	$/kg
P_f	1.000	$/kg
p_fuel	3.8x10^-9	$/J
p_CW	2.22x10^-10	$/J
p_pow	5.6x10^-5	$/J
p_vap	2.4x10^-9	$/J

Brasil

Brasil

A NEW BENCHMARK FOR PLANTWIDE PROCESS CONTROL

Abstract

An	Aromatic hydrocarbon compound with n carbons
An⁺	Cut composed of aromatic hydrocarbons with n carbon atoms of the lighter component
An^-	Cut composed of aromatic hydrocarbons with n carbon atoms of the heavier component
Cn	Hydrocarbon compound with n carbon atoms
Cn⁺	Cut composed of hydrocarbons with n carbon atoms of the lighter component
Cn^-	Cut composed of hydrocarbons with n carbon atoms of the heavier component
c	Controlled variable
u	Manipulated variable
d	Disturbance variable
c_s	Controlled variable reference value
J	Objective function
K_c	Proportional gain
τ_I	Integral time constant