sv-lncs€¦  · Web viewThe production and utilization of high pressure syngas (in a pre-combustion IGCC power plant) is well suited for CO2 absorption 14, 18, 19 by physical solvent

Process Design of CO2 Desorption from physical solvent Di-Methyl-Ethre of poly-Ethylene-Glycol

Ashok Dave 1, Bhumika Pathak * 2, Medha Dave 3, Sina Rezvani 4, Ye Huang 5 Neil Hewitt 5

1 Institute of Infrastructure Technology Research and Management, Ahmedabad, 2 Pramukh Swami Medical College, Karamsad, 3 California State University, Long Beach, CA, USA, 4 Mandurah Innovation, Information and Infrastructure Inc. Suite 1, 8 Donnelly Gardens,

Dudley Park, WA 6210, Australia 5 CST, Ulster University Jordanstown, Newtownabbey, Antrim, Northern Ireland, U.K. BT37 0QB{ Ashok Dave, [email protected] }

Abstract: Integrated Gasification Combined Cycle (IGCC) is a promising technology for effective control of green-house gas emission through CO2

capture pre-combustion process. This article describes the relative advantage of a novel energy efficient process configuration for desorption and compression of CO2 (previously absorbed by physical solvent Di-Methyl-Ethre of poly-Ethylene-Glycol (DMEPEG)). DMEPEG is a blend of several polymeric chain length (n = 3 to 9) of CH3-O-[C2H4O]n-CH3 which is a polar organic liquid solvent.

Desorption of dissolved CO2 from solvent at highest possible pressure is helpful to minimize the power consumption for subsequent compression of CO2. This article quantifies the effect of heating the DMEPEG solvent to 120 °C for CO2

desorption (compared to CO2 desorption at 35 °C) on the regeneration (desorption) of CO2 at various pressure stages.

CO2 desorption performance of DMEPEG solvent is assessed using ProTreat® simulation software. Depressurization of 4.455 kmol/s DMEPEG solvent (with dissolved gas) beginning at 120 °C results in desorption of 2.077 kmol/s CO2

capture (91.4 kg/s) out of initially dissolved 2.194 kmol/s CO2 (94.66 %). Solvent heating upto 120 °C (instead of 35 °C) can compress the 97.1 kg/s CO2

from 3 barA to 34.7 barA consuming 6 MW (instead of 8.15 MW) power for CO2 compression, thus resulting in 15 % saving for CO2 compression upto 120 barA consuming 14.1 MW power consumption.

Keywords: DMEPEG, CO2 Desorption, CO2 Capture

1 Introduction

CO2 capture from large point source is considered to be an effective method of mitigation of challenges posed by greenhouse effect and global warming. However, despite the maturity and experience of these technologies at appropriate scale, it could not be deployed in sufficient number due to the requirement of additional investment and energy consumption, thus raising the cost of energy. Advantage of energy saving for compression of CO2 (resulting from desorption of CO2 at higher pressure –

facilitated by heating of rich solvent above the absorption temperature) has been quantified to facilitate the FEED study or the Techno-Economic Assessment.

Also there is significant novelty premium attached to the technologies for CO2 capture due to novelty of process coupled with lack of operational experience and confidence. Highlighting the effect of variation of process parameters can be helpful to make the process energy efficient and to facilitate the selection and sizing of equipment. The overarching aim of this work is to estimate the scale of various equipment size, solvent circulation and energy interaction to estimate the CAPEX and OPEX and its realistic effect on the overall techno-economic performance of the (pre-combustion) IGCC technology.

The process of pumping and heating / cooling solvent and the process of compression of separated CO2 are two major energy guzzlers of the solvent based CO2 capture process. These have to be closely integrated and efficiently carried out to optimize the overall energy consumption of CO2 capture.

The production and utilization of high pressure syngas (in a pre-combustion IGCC power plant) is well suited for CO2 absorption 14, 18, 19 by physical solvent (such as di-methyl-ether of poly-ethylene-glycol - abbreviated as DMEPEG) because CO2

absorption in physical solvent is in direct proportion of the partial pressure of CO 2 in syngas. Once the CO2 is absorbed in a physical solvent, its efficient desorption (by depressurization of physical solvent) is important in terms of overall plant design and utility consumption. This article describes a novel process configuration for integrated and energy efficient desorption of CO2 followed by its compression.

2 Literature Review

The Gasifiers producing syngas are operated at high pressure in the interest of syngas quality and economy. The physical solvents are better placed than chemical solvent to treat the syngas produced at high pressure. This article concerns the integration of the process of CO2 desorption (followed by its compression) with the overall CO2 capture process.

Literature 22 discusses the prominent solvent technologies and process modeling techniques. Relative performance and ease of operation has been compared 20 for prominent physical solvent such as DEPG (or DMEPEG or trade name of Selexol® solvent), Methanol (trade name of Rectisol® solvent), Propylene Carbonate (trade name of Fluor® solvent) and NMP (N-Methyl 2-Pyrolidone or trade name of Purisol®). These comparisons reveal the superiority of DMEPEG (Selexol®) solvent in terms of lower solvent loss (due to lower vapor pressure), simplicity of the process, suitability for operations with all the major constituents of syngas (selective to H2S and suitable for CO2, H2S, CH4, COS, HCN, etc.) and wider range of operating temperature.

The DMEPEG solvent is a blend of glycol ethers with various polymer chain lengths (n). The general formula of DMEPEG is CH3-O-[C2H4O]n-CH3. The molecular mass

of DMEPEG solvent is the weighted mean of molecular mass of its constituent species, which, for this research, is considered as 280 g/mole.

Equilibrium capacity of DMEPEG (Selexol®) solvent to absorb CO2 13 has been compared with that of Sulfolane ® 21 solvent. The Henry coefficient for binary solution of these solvent with CO2 is mentioned in Figure 1a and Figure 1b below. For DMEPEG solvent in the temperature range of 20 °C to 70 °C for CO2 partial pressure up to 45 barA, the Henry’s Number (KH, bar) is in the range of 20 to 100. For Sulfolane® solvent in the temperature range of 30 °C to 110 °C, the Henry’s Number (KH, bar) is in the range of 100 to 500. These data reveal the superior CO2

absorption capacity of Selexol® solvent in comparison to Sulfolane® solvent. Also the Selexol® solvent is non-corrosive and non-toxic. Besides undertaking the bulk CO2 capture, it can also undertake the H2S capture up to trace (ppm) level.

Physical solvents DMEPEG (Di Methyl Ether of Poly Ethylene Glycol) is suitable for acid gas removal from syngas in a pre-combustion IGCC power plant due to its affinity to absorb gas components such as H2S and CO2 and also because of the fact that their solubility in physical solvent is in direct proportion to their partial pressure in the syngas. The advantages of DMEPEG solvent are extensively discussed in the literature.

Figure 1a Henry’s Number for DMEPEG solvent

Figure 1b Henry’s Number for CO2 dissolved in prominent physical solvent (including Sulfolane)

3 Objective

Objective of this research is to develop a detailed process model for CO2 desorption by DMEPEG solvent (to enable detailed techno-economic assessment by bottom up approach). CO2 desorption performance of DMEPEG solvent is assessed using ProTreat® simulation software. The effect of solvent temperature is analyzed for its effect on gas desorption from depressurized solvent. The power consumption for compression of the quantity of CO2 desorbed at various individual pressure stages has been estimated as per Table 1.

4 Process description

The proposed process configuration is described using the process flow diagram (PFD) in Figure 2. Depressurization of CO2 rich solvent causes the absorbed CO2 to get desorbed. Hydraulic Power Recovery Turbine (HPRT) recovers the power from depressurizing solvent. The depressurized solvent is taken to Flash Tank to allow sufficient residence time for the mixture of dissolved gas (predominantly CO2) to get separated from the liquid solvent. The liquid solvent from Flash Tank is taken to next stage of HPRT to continue further depressurization of solvent. The solvent from Flash Tank – 4 is cooled for recirculation for CO2 Absorption and Capture in a continuous cycle.

Figure 2 Process Flow Diagram (PFD) of CO2 Desorption and Compression

This process configuration has been designed to suit the Shell Coal Gasification (SCGP) process producing clean syngas at 35 to 40 bar pressure and economic consideration. The process temperature is governed by the aspects such as solubility (of gases in DMEPEG solvent), and safety etc.

The CO2 rich gaseous stream emerging from these Flash Tank (1 up to 4) is cooled (causing pressure drop) from 120 °C to 30 °C for compression in an integrally geared compressor up to 120 barA to facilitate its transportation. The CO2 being compressed is also intercooled at various stages to optimize the power consumption for compression. The CO2 compressed by each stage of the compressor is mixed together with the incoming stream of desorbed CO2 for cooling together which also causes pressure drop.

Solvent de-pressurization at 120 °C (or 35 °C) causes the following amount of CO 2 to be desorbed at respective pressure. The amount of CO2 desorbed from depressurizing DMEPEG solvent at 120 °C (or 35 °C) at each stage is mentioned in Table 1. The amount (kmol/s converted to kg/s) of CO2 to be compressed at each pressure stage together with the pressure value at inlet and outlet of each compression stage enables the estimation of power consumption for compression for respective stages as per Table 1. The energy input requirement for compression of this desorbed CO2 up to 34.7 bara (beginning at 300 K) has also been estimated. The following assumptions have been made to estimate the power consumption. Polytropic index of compression ( κ ) for CO2 = 1.28. Initial Temperature for each compression stage (after

intercooling) = 300 K. Gas constant ( R ) = 0.18895 kJ/kg-K. Molecular mass of CO2 to be compressed = 44 gm/mole. Polytropic Efficiency (of Compression) = 83 %. CO2 is compressed up to 120 barA to facilitate it’s transport and consumption. To compress the CO2 up to 34.7 barA, 5.996 MW power is consume if the CO2 is desorbed at 120 °C whereas 8.15 MW power is consumed if the CO2 is desorbed at 35 °C. Reputed OEM has quoted the Integrally Geared Compressor for this service to compress these flowrate of CO2 at respective pressure up to 120 barA by consuming 14.1 MW power. The additional power consumption of ((8.15-5.996)/14.1 = 15.27 %) due to solvent depressurization (and CO2 desorption) at 35 °C (instead of 120 °C) is described in the Table 1 below. 1

Table 1 Power consumption for compression of the quantity of CO2 desorbed at various individual pressure stages

Stage No.

CO2 Desorption (kmps) CO2 to be

compressed (kg/s)

Compression Pressure (barA)

Power consumption

(MW)Solvent

at 35 °C

Solvent at 120

°Cinput Output 120

°C 35 °C

1a 0.430 0.538 18.927 3 5.5 0.838 1.0481b 0.430 0.538 18.927 5.4 11.4 1.049 1.3132 0.438 0.665 38.213 10.9 20.5 1.768 2.4483 0.358 0.494 53.955 20 28.4 1.343 1.8584 0.261 0.510 65.437 27.9 34.7 0.998 1.4825 0.720 0 97.101 34.7

TOTAL 97.101 3 34.7 5.996 8.150

5 Simulation by and Validation of ProTreat software

CO2 absorption process is modeled as a steady state simulation using ProTreat software (Version 5.2, 2013). The non-ionic gas solubility model for DMEPEG solvent available within ProTreat software is utilized for rate based simulation of solvent Depressurization and CO2 Desorption. Characteristics of DMEPEG solvent and its validation for ProTreat software (Version 5.2, 2013) is discussed in literature 1,

2, 13.

6 Property Data and Simulation

The non-ionic liquid package in ProTreat software (for simulation of acid gas capture by physical solvent) consists of various thermodynamic models to describe the gas phase, the physical solvent in liquid phases, and their interaction. In ProTreat software, the non-ionic liquid package uses an activity coefficient representation of Henry’s law for the liquid and the Peng-Robinson equations of state (EOS) for the vapour. Gas solubility in DMEPEG solvent as per Non Ionic Liquid model

implemented in ProTreat software (Version 5.2, 2013) is considered for this publication. Gas solubility 15, 16, 17 in DMEPEG solvent depends on solvent composition as well. The exact composition of the DMEPEG blend implemented within ProTreat software is kept confidential by Optimized Gas Treating, Inc.(OGT). As per OGT, the solubility model is based on publications 3, 4, 5, 6, 7, 8 as the source of the solubility model implemented within the ProTreat software (Version 5.2, 2013).

Figure 3: Isothermal property data for CO2 dissolved in DMEPEG solvent at Equilibrium (saturated solvent)

Figure 4: Solubility data for CO2 dissolved in DMEPEG solvent at desorption induced equilibrium (saturated solvent) for depressurization beginning at 37 barA and initial temperature being 35 / 70 / 120 °C

The solubility data (for binary system of CO2 dissolved in DMEPEG solvent) derived using the solubility model implemented within ProTreat software (Version 5.2, 2013) is compared 9, with published data (UniSim_Ahn (Edinburgh)_2014 10, Xu_1992 11, Gainar_1995 12, Henni_2005 13) for solubility of CO2 in different blend of DMEPEG solvent (and its individual species). Isothermal property data for the binary solution of CO2 dissolved in DMEPEG solvent (derived from the ProTreat software (Version 5.2, 2013)) is described in the Figure 3. Isothermal solubility of CO 2 in DMEPEG solvent (at 35 °C, 70 °C and 120 °C) is described in terms of the mole fraction of CO2 and DMEPEG at saturation (equilibrium) and the Henry’s number (KH, bar) in Figure 3.

Here it is important to mention that the solvent temperature falls upon gas desorption (due to latent heat loss with desorbing gas). The CO2 desorption from DMEPEG solvent is described below as a function of temperature and pressure. The initial temperature is in the following order: 120 °C, 70 °C or 35 °C. The initial pressure is 37 barA. Figure 4 shows the solubility of CO2 in the DMEPEG solvent in relation to a progressive reduction in solvent temperatures and pressures. Protreat calculates the amount of remaining CO2 in the solvent after each pressure reduction stage. Based on this calculation, the CO2 desorption can be quantified for different pressure and temperature conditions.

The comparison of CO2 dissolving capacity of binary system within the multi-component system is shown in Figure 5. The partial pressure of CO2 in the gas phase is given by the primary X axis and the mole fraction of CO2 in liquid phase is

presented on the Y axis. The partial pressure of H2O (water vapor) is described on the secondary X axis and the mole fraction of H2O (dissolved water) in the liquid phase is depicted on the secondary Y axis.

The partial pressure of the released gas is positively correlated to the solvent pressures. This means that the partial pressure of CO2 will be lower after any solvent depressurization. In Figure 5, the reduction of partial pressure of CO2 is described by the primary X axis from right to left. The Figure also shows the reduction of partial pressure of H2O as water vapor. This is given by the secondary X axis from left to right. In contrast to the drop of CO2 mole fractions in the solvent after the depressurization, the mole fraction of H2O in liquid phases increases despite decreasing partial pressure of H2O (water vapor)

Figure 5: Property data for CO2 dissolved in DMEPEG solvent at Equilibrium (saturated solvent) for depressurization beginning from 120 C (comparison on Binary system with Multi-component system)

The mole-fraction of water dissolved in DMEPEG solvent is in the range of 19 % to 24 %for the multi component system. This is equivalent to the mass fraction which is between 1.9 % and 2 %.

At lower CO2 loading, this capacity of dissolving CO2 in DMEPEG solvent is similar for both – the binary system (DMEPEG + CO2) and the multi-component system (DMEPEG + Water + CO2 + other syngas constituent). However, the solubility of CO2 decreases with the rise in the amount of dissolved water in the DMEPEG solvent. This is observed in the form of higher partial pressure of CO2 in the gas phase (multi-component Green • w.r.t. Binary Maroon • ) for similar mole-fraction of CO2

dissolved in the DMEPEG solvent (in liquid phase). The mole-fraction of dissolved water w.r.t the partial pressure of water vapor (multi-component, Blue • ) is also described in Figure 5.

Figure 6: CO2 dissolved in DMEPEG solvent (binary system) at 36.2 barA and desorption of CO2 from depressurizing DMEPEG solvent at various pressure stages

7 Gas Desorption (Quantity and Analysis)

Gas desorption from depressurizing solvent is affected by the species dissolved in the solvent. This phenomenon is analysed in two separate ways using the simulation results derived using the ProTreat software (Version 5.2, 2013). In the first part, the effect of solvent depressurization is described for the binary system of CO2 dissolved in DMEPEG. In the second part, the effect of solvent depressurization is explained for the multi component system of CO2 dissolved in the solvent, besides other constituent of syngas such as dissolved water (up to 17 % mole) and other syngas constituents.

7.1 Binary system

A binary system of DMEPEG solvent and CO2 is considered.

7.1.1 Initial condition (Assumption)

DMEPEG solvent saturate by dissolved CO2 at 36.2 barA, 35 C is considered as the initial condition for this analysis. At this condition, 1.418 kmol CO2 is dissolved in 1 kmol DMEPEG solvent at saturation, as shown in the Figure 4 (100 %, in Purple) below.

7.1.2 Gas desorption

Heating or Depressurization lowers the gas dissolving capacity of solvent, thus leading to desorption of dissolved gas. CO2 desorption at various pressure stage upon solvent depressurization (for binary system of CO2 dissolved in DMEPEG solvent), and the resulting temperature drop (Figure 4, based on the simulations result) is described in Figure 4. Various techniques of solvent depressurization and the resulting gas desorption are described below.

7.1.3 Comparison among desorption conditions (35 °C and 120 °C)

7.1.3.1 Solvent depressurization starting at 35 °C

The CO2 dissolved in DMEPEG Solvent (1.418 mol CO2 / mol DMEPEG at 36.2 barA, 35 °C – to start with) released upon depressurization of the solvent at each pressure stage. Gas desorption at successive pressure stage as proportion of total initially dissolved gas at saturation is - 20.85 % at 28.4 barA, 21.12 % at 20.5 barA, 24.32 % at 11.4 barA and 22.45 % at 3 barA. Thus, in total, 88.74 % of the dissolved CO2 gets desorbed from the solvent. Thus, if the solvent is depressurized from 36.2 barA to 3 barA (in steps of 7.8 to 9.1 Bar), then the CO2 desorption is in the range of 20.8 % to 24.4 % of the total CO2 dissolved initially in solvent (at saturation

condition). CO2 desorbed by this technique is shown ( • in Green ) in the Figure 4 below.

7.1.3.2 CO2 desorption upon solvent heating (from 35 °C to 120 °C)

CO2 gets desorbed from the saturated solvent at initial condition (36.2 Bar, 35 °C) when the solvent is heated or depressurized. Heating of solvent from 35 °C to 120 °C accompanied by a pressure drop (in heat exchanger) from 36.2 barA to 34.7 barA results in CO2 desorption. Out of the 1.418 mol CO2 / mol DMEPEG (dissolved initially at 36.2 BarA and 35 °C), 1.071 mol of the dissolved CO2 gets desorbed (75.54 %) by bringing the solvent to equilibrium condition at 34.7 barA, 120 °C. CO2

desorbed by this technique is shown in Figure 4 ( • in Blue ).

7.1.3.3 CO2 desorption upon solvent depressurization (beginning at 34.7 BarA, 120 °C)

Depressurization of solvent at 34.7 BarA, 120 °C causes further desorption of additional CO2 at 28.4 barA (4.35 %), 20.5 barA (5.46 %), 11.4 barA (6.29 %) and 3 barA (5.81 %). Thus, in total, 21.91 % of the dissolved CO2 gets desorbed by progressively decreasing the solvent pressure as described in Figure 4 ( in Blue ).

7.1.3.4 CO2 desorption upon solvent depressurization (from 36.2 BarA, 120 °C)

In this section, the Depressurization of saturated solvent at 36.2 BarA, 120 C is analysed as a hypothetical case for the purpose of comparison with the other techniques of CO2 desorption. Such depressurization of solvent results in CO2

desorption at - 28.4 barA (5.39 %), 20.5 barA (5.46 %), 11.4 barA (6.29 %) and 3 barA (5.81 %). Thus, in total, 22.95 % CO2 is desorbed at progressively decreasing pressure between 36.2 barA, 120 C to 3 barA - which is described in Figure 4 ( in Red ).

7.2. Multi-component system

Physical solvents (such as glycol ethers) are generally polar molecules, as are the contaminants of natural gas and syngas (such as H2S and CO2). The affinity of a particular gas molecule to dissolve in a particular solvent depends on the similarity of both their molecule at molecular level. This is the reason why gas absorbing solvents show different solubility to dissolve various gas components. They have a selectivity for certain gas constituents. This characteristic makes physical solvents attractive to capture various gas contaminants, each with different affinity.

The DMEPEG solvent fed to CO2 Absorber consists of dissolved water (due to steam injection in (thermal) H2S Stripper and the absorption of water vapour from Syngas).

Additionally, the incoming solvent (recycled for continuous circulation) consists of certain un-desorbed (or un-stripped) constituents of syngas. Within the CO2

Absorber, along with CO2, various other syngas constituents are absorbed in DMEPEG solvent. The amount of gas absorption (fraction of solvent saturation) depends upon the packed tower internals and the thermochemical and the hydrodynamic condition for gas absorption. This makes the system inherently multi-component (multiple species). Within this second case of assessment of CO2

desorption from DMEPEG solvent, such multi-component system is analysed (having CO2, water and other syngas constituent dissolved in DMEPEG solvent).

7.2.1 Inlet condition

For this part, the incoming solvent (for CO2 desorption at 33.1 °C) is considered to be under saturated i.e. the gas absorbing capacity (at corresponding solvent temperature and gas partial pressure) is not completely utilized. The incoming under -saturated solvent (composition13, as per Table 2 below) at 33.1 °C can be brought to its saturation condition by heating it (thus lowering its gas dissolving capacity).

Table 2 Amount and composition of incoming multi-component CO2 rich DMEPEG solvent

Composition of incoming Solvent for Desorption at 120 C

Species Water Carbon Dioxide DMPEG Others Total

k-mol/s 1.441 2.194 4.455 0.026 8.116Mole Fraction

17.755 %

27.04 % 54.896 % 0.32 % 100 %

7.2.2 Gas desorption

The H2 co-absorbed with CO2 in the DMEPEG solvent is partially recovered by heating the solvent up to about 70 to 75 C. The gas desorbed due to such heating up to 71.5 C (or up to appropriate temperature depending on process design) consists of significant proportion of co-absorbed H2 and marginal proportion of CO2.

After the H2 recovery, the heating of the solvent is continued further up to 120 C to enable the desorption of additional gas. To induce gas desorption at comparatively higher pressure, the solvent is heated without deliberately depressurizing the solvent. The gas desorbed due to heating of solvent beyond 71.5 C (after H2 recovery at about 71.5 C) consists predominantly of CO2. The CO2 rich desorbed gas at solvent temperature (partial product of CO2 capture plant at 120 °C) is diverted to cooling followed by compression followed by transportation.

The amount and composition of solvent stream (single phase liquid left after desorption of CO2 rich gas at 120 C) including un-dissolved gas (predominantly CO2) is described in Table 3. This solvent is depressurized for desorption of remaining CO2.

To induce gas desorption at comparatively higher pressure, the solvent is warmed to 120 C (resulting in pressure drop in heat exchanger – from 36.2 BarA up to 34.7 BarA). CO2 desorption from DMEPEG solvent at various intermediate pressure is described in Table 3. For multi component system of CO2 and other syngas constituents dissolved in DMEPEG solvent (for the feed composition described in Table 2), the desorption of CO2 at various stages of solvent depressurization is described in Table 3.

From the multi-component system, 32.54 % (0.714 kmol/s) of the dissolved CO 2 fed to CO2 desorption (2.194 kmol/s) is desorbed at 34.7 barA which amounts to 34.38 % of the overall CO2 capture. Totally 94.67 % of the dissolved CO2 is desorbed at various pressure stages (by depressurization the solvent up to 3 barA – as described in Table 3).

Table 3 CO2 Desorption from DMEPEG solvent for multi-component system (at various pressure stage of solvent depressurization)

Pressure of Desorbing CO2

barA 34.7 28.4 20.5 11.4 3 TOTAL

CO2 Desorption from 120 C

kmps 0.714 0.243 0.328 0.400 0.392 2.077kg/s 31.416 10.692 14.432 17.6 17.248 91.388

Desorbed CO2

fraction - %Captured 34.38 % 11.70 % 15.79 % 19.26 % 18.87 % 100 %Absorbed 32.54% 11.08% 14.95% 18.23% 17.87% 94.67%

7.2.3 Comparison among Binary system and Multi-component system for CO2 Desorption at varying desorption temperature (35 C and 120 C)

CO2 desorption performance of multi-component system is graphically described in Figure 7. It is also compared with the performance of the binary system (saturated at 35 C and 70 C). CO2 desorption performance of the following three cases are as follows:

Saturated binary system at 35 C and CO2 Desorption beginning at 35 C (Section 7.1.3.1 – for comparison purpose)

Saturated binary system at 70 C and CO2 Desorption from depressurizing solvent beginning at 120 C

Saturated multicomponent system (having 19 % to 24 % dissolved water) at 71 C and CO2 Desorption by depressurizing the solvent beginning at 120 C

For the composition of solvent feed described in Table 3, the stage wise desorption pressure and the exact amount of CO2 desorption is mentioned in Table 4 below.

Table 4 CO2 desorption at various pressure stages 15

Desorption Pressure bara 34.7 28.4 20.5 11.4 3 TOTALCO2 Desorption per mol of DMEPEG

kmps 0.160 0.055 0.074 0.090 0.088 0.466% 34.38 % 11.7 % 15.79 % 19.26 % 18.87 % 94.67 %

In Figure 7, the desorption of CO2 from 1 mol of DMEPEG is described in absolute terms (CO2 desorption in kmol/s). In Figure 7, the CO2 desorbed at each intermediate pressure is shown as proportion (%) of total CO2 desorption for the corresponding initial condition of solvent. Also the proportion of total desorbed CO2 is shown as percentage of the dissolved CO2 (in saturated DMEPEG solvent) initially fed for CO2

desorption.

Figure 7: CO2 dissolved in DMEPEG solvent (binary and multi-component system) at 36.2 barA and desorption of CO2 from depressurizing DMEPEG solvent at various pressure stages

8 Conclusion

The paper shows the significant effect of solvent temperature on the amount of dissolved gas being desorbed with or without depressurizing the solvent. The CO 2

dissolving capacity of binary system at 35 °C and 70 °C is compared with the CO 2

dissolving capacity of multi-component system at 71 °C. The analysis shows the effect of dissolved water and other dissolved gas components on the CO2 release from DMEPEG at 36.2 barA. Compared to binary systems, the marginally higher CO2

dissolving capacity in a multi-component system is detected and the resulting CO2

release after solvent de-pressurization is observed.

The dissolved CO2 is desorbed from depressurizing DMEPEG solvent at relatively higher pressure if the solvent is at relatively higher temperature. The availability of CO2 at relatively higher pressure is helpful to minimize the power consumption for further compression of CO2. Compression of 97.1 kg/s CO2 from 3 barA to 120 barA (Desorbing from Depressurizing DMEPEG solvent at 120 °C) consumes 14.1 MW power. However a similar system consumes additional 15.27 % power if the CO 2 is desorbed at relatively lower pressure from solvent at 35 °C.

Process design aimed at minimizing the energy penalty for CO2 capture is facilitated by this work, thus enabling a FEED study or techno-economic assessment for this process.

9 Acknowledgement

The Author acknowledges the support of DECARBit Project funded by European Union (FP7 Grant No. 2119171) for part of this work.

10 Abbreviation

CCS Carbon Capture and StorageDMEPEG Di Methyl Ether of Poly Ethylene GlycolIGCC Integrated Gasification Combined CycleKH Henry’s Number or Henry’s constantPFD Process Flow DiagramTPD Tonne per DayTPH Tonne per Hour

11 Conflict of Interest statement :

On behalf of all authors, the corresponding author states that there is no conflict of interest.

12 Reference

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