Development of CO2 liquefaction cycles for CO2 sequestration

doi:10.1016/j.applthermaleng.2011.09.027

Applied Thermal Engineering

Volumes 33–34, February 2012, Pages 144-156

https://doi.org/10.1016/j.applthermaleng.2011.09.027 Get rights and content

Abstract

CO₂ pressurization is a necessary component in any CO₂ capture and sequestration (CCS) where enhanced oil recovery (EOR) is to be applied. The power demand for the CO₂ pressurization process consumes about 4% from the power plant net power.

In this paper, several CO₂ pressurization methods, such as compression or liquefaction and pumping using an open cycle or closed cycles, were explored and evaluated. New CO₂ liquefaction cycles based on single refrigerant and cascade refrigerants were developed and modeled using HYSYS software. The models were validated against experimental data and/or verified against other simulation software. The liquefaction parameters were optimized for minimum overall power consumption. The considered refrigerants for CO₂ liquefaction are NH₃, CO₂, C₃H₈ and R134a. One of the developed liquefaction cycles that liquefies the CO₂ at 50 bar using NH₃ refrigerant resulted in 5.1% less power consumption than the conventional multi-stage compression cycle as well as 27.7% less power consumption than the open CO₂ liquefaction cycle.

Highlights

►We model several CO₂ pressurization methods for their evaluation. ►We develop new CO₂ liquefaction cycles and model it using HYSYS software. ►Liquefaction cycle using NH₃ consumes 5.1% less power than multi-stage compression.

Introduction

In order to mitigate the global warming, CO₂ is captured from stationary sources and sequestered in underground geological formations. Since about one third of all CO₂ emissions from fossil fuel energy sources comes from fossil fuel burning power plants, which have the highest density of CO₂ emissions in terms of mass per power output [1], they provide an appropriate target in the attempt to mitigate the global warming.

CO₂ capture and sequestration (CCS) consists of three processes: capture, which is typically done by amine absorption; transport, which is done by either pipeline or ships; and storage, which can be done in underground geological formations such as oil wells, which can be utilized for enhanced oil recovery (EOR). Among the three processes, CO₂ capture has attracted the most attention in the literature since it is more technically challenging. Since CO₂ captured in post-combustion using amine absorption is at atmospheric pressure, CO₂ needs to be pressurized to a supercritical pressure, e.g. 150 bar, before injection into an oil well for EOR. As for storage or shipping in tankers, the captured CO₂ is liquefied at a pressure of about 6 bar so that its volume is reduced. Conventionally, CO₂ pressurization is done using multi-stage compression with intercooling. CO₂ compression consumes about 100 kWh/ton CO₂ [2] while the energy efficiency of a power plant can be decreased by 3–4% points [3]. The other pressurization approach is to liquefy the CO₂ and pump it to the target injection pressure, and then the pressurized CO₂ is evaporated so that phase change does not occur inside the well. The two approaches are shown in Fig. 1.

Many studies in the open literature developed models for the CO₂ compression process. Amrollahi et al. [4] used GT PRO software [5] to model a CO₂ compression cycle. Pfaff et al. [6] and Cifre et al. [3] used EBSILON software [7] to model a CO₂ compression cycle. Sanpasertparnich et al. [8] used an in-house code to model a CO₂ compression cycle. Moller et al. [2] used IPSEpro software [9] to model a CO₂ compression cycle. Romeo et al. [10] modeled and optimized CO₂ compression processes using EES software [11].

Few authors investigated the CO₂ liquefaction process. Aspelund et al. [12], [13] studied CO₂ liquefaction for ship transport. They considered three liquefaction pressures (20, 55 or 95 bars) where CO₂ is liquefied after compression by either seawater or by using an open cooling cycle that they patented. Moore et al. [14] carried out a similar study. According to Moore et al.’s preliminary analysis, a 35% reduction in power is possible when liquefying the CO₂ using absorption chillers and pumping the CO₂ instead of compressing it. Botero et al. [15] compared different compression strategies for CO₂ compression using HYSYS software [16]. They investigated using absorption chillers and cold seawater for CO₂ liquefaction at three liquefaction pressures.

Proprietary CO₂ liquefaction processes are available in some applications such as in the food and beverage industries. However, such applications of CO₂ liquefaction differ from power plant in terms of quantity and quality of feed gas and product gas. Several liquefaction cycles exist for natural gas liquefaction but they differ significantly from CO₂ liquefaction in terms of liquefaction temperature and cooling curves. While absorption chillers are a mature technology and many manufacturers exist, they have low efficiency and are considered complex and expensive [17].

There is a lack of literature in detailed comparison between CO₂ compression and CO₂ liquefaction and pumping processes. No author has carried out a comprehensive study on whether liquefying and pumping CO₂ for injection consumes less power than multi-stage CO₂ compression, and investigated the design of several CO₂ liquefaction cycles (cascade and single-refrigerant). Further, there has been no research conducted on optimizing the CO₂ liquefaction pressure, and none of the authors verified or validated their models.

The objectives of this paper are (1) to carry out a comprehensive comparison between CO₂ compression and CO₂ liquefaction and pumping processes for EOR application by developing several CO₂ liquefaction cycles and validating or verifying the developed models, (2) to optimize the CO₂ liquefaction pressure, and (3) to evaluate the performance of the open CO₂ liquefaction cycle.

Section snippets

CO₂ compression cycle

In order to inject the captured CO₂ into an oil well for EOR, it needs to be pressurized to a supercritical pressure. The injected CO₂ is in supercritical vapor state. The injection pressure used in this paper is 150 bar, which is typical for an EOR project. Pressurizing CO₂ is done using eight multi-stage centrifugal compressors with intercooling, so that it approaches isothermal compression. HYSYS process simulation software was used to model the CO₂ compression plant as shown in Fig. 2. The

Absorption chillers for CO₂ liquefaction

NH₃ absorption chillers can be used to liquefy CO₂ if there is enough waste heat. If there is 13.35 MW waste heat at 130 °C, NH₃ absorption chillers can be used to liquefy the CO₂ at −12 °C or 25 bar liquefaction pressure. The liquefaction load is 5.84 MW. The total power consumption (CO₂ compressors and pump) for this option is 4.37 MW, which is the lowest power consumption for preparing the captured CO₂ for injection (1.88 MW or 30.08% power savings as compared to the multi-stage compression).

Conventional open CO₂ liquefaction cycle

The second way to pressurize CO₂ is to liquefy it and then pump it to the desired pressure. The open CO₂ liquefaction cycle for liquefying the CO₂ from a stationary source is a patented cycle by Aspelund et al. [12]. According to Aspelund et al., the liquefaction of CO₂ is best achieved using their open CO₂ liquefaction cycle. The purpose here is to model the open CO₂ liquefaction cycle at ambient conditions equivalent as the previous models.

The working principle of the cycle is that it uses

Comparison

Table 12 lists the least power consumption for all explored options. It shows that the developed VCC that uses NH₃ as a refrigerant and recovers the cold energy in the liquefied CO₂ at the optimum liquefaction pressure consumes less energy than the conventional multi-stage compression with intercooling by 5.12%. Further, the NH₃–CO₂ cascade cycle consumes less power than the single-refrigerant cycle if the cold CO₂ energy were not recovered. Nonetheless, cascade cycles are more complex and

Conclusion

Several options were investigated for pressurizing the captured CO₂ gas for EOR applications. The investigation was carried out through development of HYSYS models with models validated in good agreements. The liquefaction of CO₂ was optimized using a generic HYSYS model coupled with the Matlab optimization tool that considers all power consumption and all recoverable cooling. The optimization results were graphed for different efficiency values which can be used as a tool to compare power

Acknowledgements

The authors would like to thank the sponsors of the Center for Environmental Energy Engineering (CEEE), University of Maryland, College Park, MD, USA and the Petroleum Institute of Abu-Dhabi, UAE, for their financial support of this research project.

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Development of CO2 liquefaction cycles for CO2 sequestration

Abstract

Highlights

Introduction

Section snippets

CO2 compression cycle

Absorption chillers for CO2 liquefaction

Conventional open CO2 liquefaction cycle

Comparison

Conclusion

Acknowledgements

Energy

Fuel

Energy

International Journal of Greenhouse Gas Control

Applied Thermal Engineering

Chemical Engineering Research and Design

International Journal of Greenhouse Gas Control

International Journal of Refrigeration

International Journal of Refrigeration

International Journal of Refrigeration

Applied Thermal Engineering

Carbon dioxide recovery and disposal from large energy systems

Annual Review of Energy and the Environment

Development of CO₂ liquefaction cycles for CO₂ sequestration

CO₂ compression cycle

Absorption chillers for CO₂ liquefaction

Conventional open CO₂ liquefaction cycle