Scholarly article on topic 'Application of Free Piston Stirling Cooler (SC) on CO2 Capture Process'

Application of Free Piston Stirling Cooler (SC) on CO2 Capture Process Academic research paper on "Chemical engineering"

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Abstract of research paper on Chemical engineering, author of scientific article — Chunfeng Song, Yutaka Kitamura, Weizhong Jiang

Abstract CO2 emission from large point sources (such as coal-fired power plant, cement and steel industry) has attracted a wide attention. During the mature available capture techniques, amine scrubbing approach has been utilized as the most successful one. Nevertheless, the energy penalty of regeneration and degradation of solvents are the main bottlenecks that limit the improvement of the capture efficiency. In this study, a novel application of free piston Stirling cooler (SC) on cryogenic CO2 capture process has been described. In the developed system, the CO2 in the gas stream can be captured in solid form under the cryogenic condition, and frosted on the cold head of SC. In order to avoid the adverse influence of frost layer, a scrapper is added beside the cold head of SC to scrap the deposited CO2 timely. Furthermore, the fallen CO2 crystals is gathered and preserved for further utilization. Compared to other cryogenic sources, the advantage of SC are high efficiency, environmental friendly, safe and convenient. The aim of this paper is to evaluate the properties of the novel system and implement a brief comparison of performance with other cryogenic method.

Academic research paper on topic "Application of Free Piston Stirling Cooler (SC) on CO2 Capture Process"

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Energy Procedia 37 (2013) 1239 - 1245

GHGT-11

Application of Free Piston Stirling Cooler (SC) on CO2

Capture Process

Chunfeng Song a, Yutaka Kitamura *a, Weizhong Jiang b

a Graduate School of Life and Environmental Sciences, University of Tsukuba, Japan b College of Water Conservancy & Civil Engineering, China Agricultural University, China

Abstract

CO2 emission from large point sources (such as coal-fired power plant, cement and steel industry) has attracted a wide attention. During the mature available capture techniques, amine scrubbing approach has been utilized as the most successful one. Nevertheless, the energy penalty of regeneration and degradation of solvents are the main bottlenecks that limit the improvement of the capture efficiency. In this study, a novel application of free piston Stirling cooler (SC) on cryogenic CO2 capture process has been described. In the developed system, the CO2 in the gas stream can be captured in solid form under the cryogenic condition, and frosted on the cold head of SC. In order to avoid the adverse influence of frost layer, a scrapper is added beside the cold head of SC to scrap the deposited CO2 timely. Furthermore, the fallen CO2 crystals is gathered and preserved for further utilization. Compared to other cryogenic sources, the advantage of SC are high efficiency, environmental friendly, safe and convenient. The aim of this paper is to evaluate the properties of the novel system and implement a brief comparison of performance with other cryogenic method.

© 2013 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of GHGT

Keywords: CO2 capture, cryogenic, Stirling cooler

1. Introduction

* Corresponding author. Tel.: +81 0298-53-4655; fax: +81 0298-53-4655. E-mail address: kitamura.yutaka.fm@u.tsukuba.ac.jp.

1876-6102 © 2013 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of GHGT doi: 10.1016/j.egypro.2013.05.222

Nowadays, climate change has become a primary problem in the word. CO2 emission from large point source (such as coal-fired power plant) is one of the most important reasons that causes this issue [1]. The main CO2 recovery methods contain: chemical absorption, physical adsorption, membrane separation and cryogenic distillation. Amine based absorption process is the most mature technique that has been commercially utilized in large CO2 emission sources (such as coal-fired power plant, iron and steel industry, cement manufacture etc.) [2]. However, there also some bottlenecks for this technique (such as high energy consumption on solvent regeneration, corrosion and degradation). For membrane techniques, the capital cost of membrane material is still high and needs to reduce [3].Cryogenic CO2 capture technologies are a promising alternative to remove CO2 from power plant flue gas. During the existing cryogenic technologies, low temperature source is mainly provided by the evaporation process of liquefied natural gas (LNG) and liquid nitrogen (LN2) [4,5]. Nevertheless, the utilization of these cryogenic sources has a high requirement on the installation and which leads to the increase in the capital cost. In light of these situations, a number of researches are implemented to improve the capture efficiency and reduce the energy consumption.

An alternative way of providing cryogenic condition is the usage of Stirling cooler (SC). SC is a typical kind high efficient chilling equipment which has been successfully used in various fields, such as infrared detectors, superconductor filters, space exploration and cryopumps [6]. Recently, this apparatus has been paid attention on CO2 recovery process due to the superior thermal performance compared with conventional refrigerants [7].In the novel system, the SC use a mechanical displacer in the cold head to expand compressed helium (He) gas and create a cryogenic condition. The novel process makes a good use of SC's advantages and provides a good efficiency and reliable range of cooling capacity. At different parts of the system, H2O and CO2 in the flue gas can be recovered in liquid and solid form respectively.

In this work, a novel application of SC on CO2 capture has been developed. The objective of the paper is to summarize the characteristics of the developed cryogenic CO2 capture system and compare with the existing cryogenic approaches.

Nomenclature

CCS CO2 capture and storage

GHG greenhouse gas

SC Stirling cooler

LN liquid nitrogen

LNG liquefied natural gas

2. Properties of the cryogenic system

The system is pre-chilled by three SCs (namely SC-1, 2 and 3) as shown in Figure 1. When the temperature achieves the required cryogenic condition, the simulated flue gas can be introduced into the system. After the gas mixture enters the cryogenic CO2 capture system, the temperature dropped promptly due to heat exchange with SC-1. When the gas stream is cooled to around 0 °C, the moisture in the flue gas will condense and exhaust from the condensate water outlet. Then, when dry gas stream passes through the cold head of SC-2, the CO2 will frost on the surface of the cold head due to the cryogenic

temperature (approximately -105 °C) maintained by SC-2. The residual gases mainly contain N2 which has a freezing point around -209.86 °C (pure N2), and therefore will flow out the system without phase change. After the CO2 is captured on the cold head of SC-2, the scrapper is used to scrape the deposited CO2. This measure can avoid the adverse influence of frost layer on the heat and mass transfer processes. Finally, the fallen CO2 can be gathered and preserved by SC-3.

□□□□

Control panel

Computer

Figure 1 Schematic diagram of SC based cryogenic CO2 capture process.

3. Experimental

The low temperature source of the system is maintained by SC. The configuration of SC is shown in Fig. 2. The cold air is absorbed from air inlet and warm air is exhausted from air outlet. During this process, the cold energy is gathered at the cold head part. The regenerator for the cooler is helium and which is environmental friendliness. The temperature of the critical positions in the system is measured by the thermometer and recorded in the control panel. Meanwhile, the temperature setting can also be implemented in the control panel. The whole CO2 deposition process is monitored by a charge coupled device (CCD) camera. In addition, the experiments are implemented in a laboratory scale. The CO2/N2 gas mixture (13/87 vol.%) is employed as the influent gas stream.

Figure 2 The structure of Stirling cooler.

4. Results and discussion

4.1 Cryogenic sources

As the most important part in cryogenic CO2 capture processes, the investigation of cryogenic sources is significant. Therefore, the comparisons of the characteristics for different cryogenic sources were conducted in this section. The comparison results are list in table 1. For the LN and LNG, the advantages are good liquidity and thus they have a large cooling area. In addition, the cryogenic temperature of LN and LNG are -196 °C and -162 °C, and which are both lower than SC (minimum is -140 °C). However, the transportation of LN and LNG is an energy penalty process and a high requirement on the installation is also necessary. Furthermore, the scale of the SC system is small. By contrast, the size of installation for LN and LNG is large.

Table 1 The comparison of the common cryogenic sources for CO2 capture

Cryogenic source Advantages Disadvantages Ref.

LN 1) good liquidity 2) rapid freezing 3) cryogenic temperature 1) high captial cost of installation 2) high production cost [4,5]

LNG 1) good liquidity 2) cryogenic temperature 1) high captial cost of installation 2) location constraint 3) flammability [8]

SC 1) high efficiency 2) convenient 3) small size 1 ) oscillation 2) limitaion of cooling area 3) long pre-chilling time present work

4.2 Cryogenic performance

The performance of the exploited system is investigated in this section. The temperature variation of SCs during the idle operating stage is shown in Figure 3. With time went on, the temperature of SCs decreased rapidly. However, due to the different function of SCs, the lowest temperatures are also different. After 240 minutes, the temperature of SC-1, 2 and 3 are -37.3, -85.4 and -109.5 °C, respectively. Meanwhile, the temperature variation process in capture period is shown in Figure 4. It indicates that when introduces the gas stream into the system, the temperature of SCs increased accordingly. For SC-1, the temperature rose from -37.4 °C to -10.2 °C. For SC-2, the temperature increased from -109.3 °C to -102.5 °C. Furthermore, for SC-3, the temperature increased from -85.6 °C to -80.1 °C. This can be explained by the fact that when the gas mixture inflows into the system, the CO2 can sublimate and frost onto the surface of cold head under the cryogenic condition. The frosted CO2 adversely affected the heat transfer process. Therefore, the temperature of SCs would rose up accordingly. The detail temperature variation process of the system has been introduced in our previous work [9].

Figure 3 Temperature variation process during the idle operating period

-10 -20 -30

<1) cp

I -70 H

-80 -90 -100 -110

0 2 4 6 8 10 12 14 16 18 20 Capture time (min)

Figure 4 Temperature variation process during the capture period

5. Conclusion

The cryogenic flue gas capture technology under development offers a new approach for mitigating CO2 from power plant. It focuses on the application of Stirling cooler on CO2 separation. When the temperature in the system decreased to the condition below the frost point of CO2 by SC, the CO2 in the flue gas can desublimate into dry ice with other non-greenhouse gas exhausting from the outlet. In previous studies on cryogenic CO2 capture techniques, the most important drawback is high energy consumption. Nevertheless, the application of SC can avoid the difficulty due to the high efficiency itself.

In the present system, it needs to take around 240 minutes to pre-chill the system to the required temperature and which is time-consuming and energy consumption. For the future work, the system should be improved to reduce the requirement on the condition. The integration with other techniques (such as amine scrubbing, membrane and pressure swing adsorption) is also an effective approach. In addition, the oscillation of SC would lead to the energy loss and generate a tremendous challenge to the tightness of the system. Therefore, the structure of the system should also be improved and some vibration-proof material can be utilized.

Acknowledgements

The authors acknowledge the funding provided by the Japan Science and Technology Agency (JST) for Transfer Program through the target driven R&D (AS2115051D). We thank Mr. Yamano and Mr. Yamasaki in TANABE ENGINEERING for their help on technology.

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