US 12,533,627 B2 · Low-cost and high-efficiency absorption-desorption decoupling method for contaminant-CO2 synergistic capture

Abstract

The invention relates to a low-cost and high-efficiency absorption-desorption decoupling method for contaminant-CO2 synergistic capture. According to the method, an optimization model of absorption-desorption decoupling control for contaminant-CO2 synergistic capture under different working conditions is built, the optimization objective is to obtain high-purity liquid contaminants and CO2 at low cost and efficiently, and an adaptive penalty function is constructed to transform a solution of a constrained optimization problem into that of an unconstrained optimization problem, thereby controlling parameters in a real-time, precise and stable manner. Moreover, supported by means of flue gas pre-scrubbing and cooling, multi-stage intercooling and column-top demisting, the method of the present invention achieves efficient capture of contaminants and CO2. According to the invention, the absorption process is decoupled from the desorption process, and the coordinated control of temperature-pH-liquid-gas ratio and rich liquid flow-desorption temperature in all cycles is carried out to realize the synergistic capture-regeneration-concentration of contaminants and CO2 with high efficiency and low energy consumption, thereby reducing the high cost of the traditional method where a flue gas cleaning system and a carbon capture system operate separately.

An absorption-desorption decoupling method for contaminant-CO2 synergistic capture, wherein flue gas enters an absorption system which comprises a multi-cycle absorption column, and then enters a first-cycle contaminant absorption section, a second-cycle CO2 absorption section, a third-cycle CO2 absorption section and a fourth-cycle water washing section in sequence after passing through a pre-scrubbing section arranged at a front part of the multi-cycle absorption column;

rich liquid enters a desorption system which comprises a desorption column via a lean-rich liquid heat exchanger, and lean liquid goes out of the desorption column and enters the lean-rich liquid heat exchanger;
regenerated vapor in the desorption column enters a separation and purification system;
the absorption system and the desorption system are respectively controlled by a decoupling control system;
the decoupling control system comprises an absorption control unit for the multi-cycle absorption column and a desorption control unit for the desorption column;
the absorption control unit comprises a first-cycle control unit, a second-cycle control unit, a third-cycle control unit, a fourth-cycle control unit and an absorbent preparation unit;
the absorption-desorption decoupling method comprises:
(1) decoupling of four cycles in the absorption system, wherein the absorption process is divided into four parts by controlling the four cycles in different areas;
a first cycle corresponds to a bottom layer of the multi-cycle absorption column and is configured to absorb contaminants and be independently controlled to ensure the contaminant removal efficiency;
a second cycle corresponds to a second layer of the multi-cycle absorption column and is configured to absorb CO2 and be independently controlled to increase the CO2 load of an absorbent;
a third cycle corresponds to a third layer of the multi-cycle absorption column and is configured to absorb CO2 and be independently controlled to ensure the CO2 absorption efficiency;
a forth cycle corresponds to a top layer of the multi-cycle absorption column and is configured to remove aerosols and be independently controlled to ensure that the emission of flue gas aerosols reaches a preset standard;
and (2) decoupling of the absorption system and the desorption system, wherein the multi-cycle absorption is adopted so that the absorption liquid entering the desorption column is in a saturated state, thereby reducing the influence of the absorption process on the desorption;
the absorption-desorption decoupling method specifically comprises the following steps:
(1) building a database based on real-time data and historical data of three-path parameters including cooling water path, absorption liquid path and flue gas path, wherein the parameters include flue gas flow (G), partial pressures (pout) and (pin) of gas in flue gas, the concentration (cab) of an absorbent, the pH value (pHi), temperature (Ti) and flow (Li) of liquid in a cycle, the pH value (pHrich), temperature (Trich), and flow (Lrich) of rich liquid entering the desorption column, the pH value (pHlean) and temperature (Tlean) of lean liquid leaving the desorption column, the concentrations, (cpa), (csa) and (cta) of primary amine, secondary amine, and tertiary amine in fresh absorption liquid, and the heat load (W) of a reboiler;
(2) building, on the basis of the built database, an optimization model of absorption-desorption decoupling control for contaminant-CO2 synergistic capture under different working conditions;
according to an actual operation of the absorption system and the desorption system, setting constraints for adjustment ranges of operating parameters as:
ηCO2≥ηset,CO2
ηcont≥ηset,cont
Gmax≥G≥Gmin
pin,max≥pin≥pin,min
cab,max≥cab≥cab,min
pHi,max≥pHi≥pHi,min, i∈[1,4]
Ti,max≥Ti≥Ti,min, i∈[1,4]
Li,max≥Li≥Li,min, i∈[1,4]
wherein ηCO2 and ηset,CO2 represent the removal efficiency and set efficiency of CO2, respectively and ηcont and ηset,cont represent the removal efficiency and set efficiency of a contaminant, respectively;
key parameter models for control of the first-cycle control unit, the second-cycle control unit, the third-cycle control unit, the fourth-cycle control unit, the absorbent preparation unit and the desorption control unit are:
η1st=fabsorbent,cont,1st(pH1,T1,L1)
η2nd=fabsorbent,co2,2nd(pH2,T2,L2)
η3rd=fabsorbent,co2,3rd(pH3,T3,L3)
η4th=fwater,4th(pH4,T4,L4)
ηabsorbent=fabsorbent(cpa,csa,cta)
ηdesorption=fdesorption(Lrich,W)
wherein η1st, η2nd, η3rd, η4th, ηabsorbent and ηdesorption represent efficiencies of the first-cycle control unit, the second-cycle control unit, the third-cycle control unit, the fourth-cycle control unit, the absorbent preparation unit and the desorption control unit, respectively;
adopting following particle fitness function (Fitness) as an objective function of the optimization model and combining constraints of the operating parameters to achieve parameter optimization as follows:
Fitness=costmin=cost1st+cost2nd+cost3rd+cost4th+costabsorbent+costdesorption
wherein cost1st, cost2nd, cost3rd, cost4th, costabsorbent, and costdesorption represent energy and material consumption costs of the first-cycle control unit, the second-cycle control unit, the third-cycle control unit, the fourth-cycle control unit, the absorbent preparation unit and the desorption control unit, respectively;
(3) constructing a penalty function (Penalty) and adding the penalty function (Penalty) to an objective function Fitness(x);
transforming a solution of a constrained optimization problem into that of an unconstrained optimization problem through a penalty strategy of the objective function;
and using self information and population information obtained during a particle evolution iteration process as feedback conditions to dynamically adjust a penalty coefficient of the particle fitness beyond a feasible range after each iteration;
x
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cost
1
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,
cost
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cost
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cost
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cost
absorbent
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cost
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Fitness
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f
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Penalty
Penalty
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β
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λ
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λ
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otherwise
wherein x represents optimization objective;
Penalty represents the penalty function;
λ represents adaptive factor;
Gp represents layered penalty coefficient;
ηi represents the removal efficiency of a unit that is in operation;
ηseti represents the target efficiency of the unit that is in operation;
t represents the number of iterations;
μ, ε1, β1 and β2 represent scale factors of the penalty function;
ε2 and α represent power factors of the penalty function;
RELU (rectified linear unit) represents an activation function judgment module and RELU(x)=max(0, x);
β1>β2>1;
case1 represents a case where all the optimal individuals are feasible solutions in the iteration process;
case2 represents a case where there is no feasible solution in optimal individuals during the iteration process;
and
(4) after obtaining a parameter combination of first-cycle control, second-cycle control, third-cycle control, fourth-cycle control, absorbent preparation and desorption control, with the parameter combination as a control target, carrying out an advanced control method comprising predictive control and fuzzy control to control parameters in real-time, thereby ensuring that the efficiency of absorption-desorption decoupling for contaminant-CO2 synergistic capture reaches the preset standard.

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Low-cost and high-efficiency absorption-desorption decoupling method for contaminant-CO2 synergistic capture

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Low-cost and high-efficiency absorption-desorption decoupling method for contaminant-CO2 synergistic capture

Life of this patent

Abstract

Claims9