Concentrated Aqueous Piperazine as CO2 Capture Solvent: Detailed Evaluation of the Integration with a Power Plant☆

AbstractAn integrated energetic evaluation has been performed of a reference coal-fired power plant, a power plant with an advanced MEA-based post-combustion CO2 capture plant, and a power plant with a capture plant using concentrated piperazine (PZ) and high-pressure flash regeneration. This comparison shows that using a MEA-based capture plant reduces the net electric efficiency from 44.6% to 35.5%, while the PZ-based capture plant reduces it to 37.4%, corresponding to an efficiency penalty of only 7.2%

Analysis of Process Configurations for CO2 Capture by Precipitating Amino Acid Solvents

Precipitating amino acid solvents are an alternative to conventional amine scrubbing for CO2 capture from flue gas. Process operation with these solvents leads to the formation of precipitates during absorption that need to be re-dissolved prior to desorption of CO2. The process configuration is crucial for the successful application of these solvents. Different process configurations have been analyzed in this work, including a full analysis of the baseline operating conditions (based on potassium taurate), the addition of lean vapor compression, multiple absorber feeds, and the use of different amino acids as alternative solvents to the baseline based on potassium taurate. The analysis is carried out with an equilibrium model of the process that approximates the thermodynamics of the solvents considered. The results show that the precipitating amino acid solvents can reduce the reboiler duty needed to regenerate the solvent with respect to a conventional MEA process. However, this reduction is accompanied by an expenditure in lower grade energy needed to dissolve the precipitates. To successfully implement these processes into power plants, an internal recycle of the rich stream is necessary. This configuration, known as DECAB Plus, can lower the overall energy use of the capture process, which includes the energy needed to regenerate the solvent, the energy needed to dissolve the precipitates, and the energy needed to compress the CO2 to 110 bar. With respect to the energy efficiency, the DECAB Plus with lean vapor compression configuration is the best configuration based on potassium taurate, which reduces the reboiler duty for regeneration by 45% with respect to conventional MEA. Retrofitting this process into a coal fired power plant will result in overall energy savings of 15% with respect to the conventional MEA process, including compression of the CO2 stream to 110 bar. Potassium alanate was found to reduce the energy use with respect to potassium taurate under similar process configurations. Therefore, the investigation of potassium alanate in a DECAB Plus configuration is highly recommended, since it can reduce the energy requirements of the best process configuration based on potassium taurat

Heat-integrated liquid-desorption exchanger (HILDE) for CO2 desorption

A novel type of separating heat exchanger, called a heat-integrated liquid-desorption exchanger (HILDE), applied to a typical CO2 desorption process, has been investigated both numerically and experimentally. Process simulations, hydrodynamic and mass transfer experiments, and a preliminary cost evaluation have been used to compare HILDE to the conventionally used combination of a separate heat exchanger and desorber equipped with structured packing. The comparison revealed that the operational costs of the HILDE are 15% lower compared to the conventional desorption configuration, while the equipment costs are 45% lower. The reduction in operational costs is mainly caused by a reduced reboiler duty. The absence of a separate desorber column and a large decrease in the condenser size are the main reasons for the reduced equipment costs. Additionally, the system volume, mass hold-up, and total contact area are also expected to be significantly lower for HILDE

Calorimetric Studies of Precipitating Solvent System

Calorimetric study of a precipitating solvent system of Potassium-Taurate (KTAU) was performed in the CPA202 calorimeter. Two different experiments were conducted, i.e. heat of absorption of CO2 in KTAU solvent at different conditions (concentration = 1.5 M and 3.0 M), loading up to ∼ 0.8 mol CO2/ mol Taurine and temperature = 25 °C, 40 °C, 80 °C). Moreover, dissolution heats of Taurine/solid were also measured. The result agrees well with the reported data. The procedure developed for the heat of dissolution measurements was verified by measuring heat of dissolution of solid Taurine in water and comparing results with data in literature. The solid formation occurs during the absorption of CO2 in 3.0 M KTAU at low temperatures (25 °C and 40 °C) and at loadings (∼ 0.3 mol CO2/ mol Taurine). The heat of dissolution of the formed solid in pure water is slightly higher than that of Taurine in pure water but less heat is required to dissolve the same solids in unloaded 3.0 M KTAU solution.publishedVersio

Integration of a high-pressure piperazine capture plant with a power plant: an energetic evaluation

Post-combustion CO2 capture can have a significant contribution to the reduction of CO2 emissions. However, it also requires a considerable amount of energy, causing a significant decrease in the net electricity output of the power plant it is associated with. A vast array of research initiatives is currently aimed at reducing this decrease. One of the main approaches is the development of improved solvents, replacing the conventionally used 30 wt% aqueous mono-ethanolamine (MEA) solution. Recently, Rochelle et al. [1] reported on the use of aqueous piperazine (PZ) and concluded that it could be the new standard solvent for CO2 capture. One of the discussed advantages of PZ is its thermal stability, allowing the regeneration step of the absorption process to be done at a temperature of 150 °C, instead of the 120 °C which is typically used for MEA solutions. This increased regeneration temperature, in combination with a higher CO2 desorption pressure, is claimed to allow a better energy performance of the capture plant. In the current work, we perform a more-detailed analyses of the energetic performance of a 1000 MWel coal-fired power plant in combination with a post-combustion CO2 capture process using 40 wt% aqueous PZ as solvent. Similar to the work by de Miguel Mercader et al. [2], the energy penalty will be evaluated by the integrated use of two types of model approaches. In this work, the capture plant is modeled in detail using Aspen Plus, while the power plant and CO2 compression are modeled with a high-level approach using efficiency performance curves that are based on a combination of fundamental and empirical relations. For the power plant, these curves give the operational envelope of the plant and describe the plant efficiency as function of power plant load and thermal energy withdrawal characteristics

Inline monitoring of CO2 absorption processes using simple analytical techniques and multivariate modeling

The solvent and the dissolved CO2 concentrations are two essential properties of CO2 absorption processes. Currently, they are typically monitored using time-consuming offline analytical techniques. Initial development efforts aiming at a cost-effective and reliable inline monitoring system are described. Using a fractional factorial experimental design covering six solvent properties and five analytical techniques, it is demonstrated that the CO2 and solvent concentrations correlate well with the density and refractive index. Applying a simplistic multivariate model to solvent samples from an industrial pilot plant indicated good potential for predictive use. Future work should focus on the development of a more accurate multivariate model, on the modeling of more solvents, and on combining the results with available process data. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In-line monitoring of solvent and CO2 properties: preliminary assessment using design of experiment

Removing acid gases such as CO2 and H2S from a gas mixture is nowadays often done using an absorption process. Two essential operating variables of such a process are the amount of active absorbent present in the solvent mixture and the amount of absorbed acid gas. Normally, the solvent concentration and the acid gas loading are measured by means of regular sample withdrawals and subsequent analysis in a laboratory. This procedure is both laborious as well as time consuming. In addition, the measurement results are not suitable for direct operational purposes; they can only be used for long term solvent and process monitoring. To enable the real-time measurement of both the solvent concentration and acid gas loading, attempts have been made to use Fourier transform infrared (FTIR) spectroscopy in combination with a multivariate analysis method, also known as chemometrics [1][2]. The use of FTIR spectroscopy showed promising results with respect to predicted solvent concentration and acid gas loading. However, some clear disadvantages exist related to the cost of the apparatus, the requirement for the apparatus to be located within a few meters of the measurement location, and the sensitivity for mixture components that the method is not (properly) calibrated for. The goal of this work is to assess whether (combinations of) other simpler analysis techniques exist that can overcome these disadvantages, for example pH or density measurements

Membrane distillation against a pressure difference

Membrane distillation is an attractive technology for production of fresh water from seawater. The MemPower® concept, studied in this work, uses available heat (86 °C) to produce pressurized water (2.2 bar and 46 °C) by membrane distillation, which again can be used to power a turbine for co-production of electricity. We develop a non-equilibrium thermodynamic model to accurately describe the transfer at the liquid-membrane interfaces, as well as through the hydrophobic membrane. The model can explain the observed mass flux, and shows that 85% of the energy is dissipated at the membrane-permeate interface. It appears that the system's performance will benefit from a lower interface resistance to heat transfer, in particular at the permeate side of the membrane. The nature of the membrane polymer and the pore diameter may play a role in this context