Compression Costs Research Articles

Mixture optimization of mechanical, economical, and environmental objectives for sustainable recycled aggregate concrete based on machine learning and metaheuristic algorithms

Recycled aggregate concrete (RAC) has received rapidly growing attention given its contribution to sustainability in the construction industry. Except for material properties, eco-friendliness and energy savings gained increasing concern during concrete production. This paper proposed a framework for mixture proportions optimization of RAC based on machine learning and metaheuristics. Six machine learning models were developed to predict the compressive strength of RAC based on a dataset with 1305 samples. With the best prediction model, three scenarios with four objective functions including compressive strength, materials cost, carbon footprint, and energy intensity of RAC were optimized using the competitive mechanism-based multi-objective particle swarm optimization (CMOPSO) algorithm. Results show all machine learning models can predict the compressive strength of RAC with high accuracy, among which the extreme gradient boosting model shows superior performance over other models. The curing age, cement content, and replacement ratio of recycled coarse aggregate are dominant features influencing the compressive strength of RAC. The CMOPSO algorithm can obtain the Pareto optimal solutions in three design scenarios. The proposed framework improves the efficiency in optimizing the mixture design of RAC for achieving required mechanical, economic, and environmental objectives.

Preparation of controlled low-strength materials from alkali-excited red mud-slag-iron tailings sand and a study of the reaction mechanism.

To address the low utilization of fines in iron tailings sand (IOTs), a controlled low-strength material (CLSM) was prepared from a combination of fine IOTs and red mud (RM) slag. The 7-day unconfined compressive strength (7-d UCS), slump and cost were used as evaluation indicators, and 16 sets of tests were designed with the Box-Behnken design (BBD) response surface method. X-ray diffraction (XRD), Fourier transform infrared (FTIR), and scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS) were used to study the microscopic morphology and reaction mechanism of the CLSM samples made with the optimal ratios. The results show that the best matching ratio for the alkali-activated RM-slag-IOTs CLSM was a sand ratio of 0.797, an NaOH dose of 3.667% and a mass concentration of 80.657%, and the 7d-UCS, slump and cost indicators verified the feasibility of applying the CLSM to the base course of pavement. Alkali activation of the CLSM also showed that the RM-slag cementation system produced new substances. Internal calcium-silicate-hydrogel (C-S-H) and calcium-aluminosilicate-hydrogel (C-A-S-H) agglomerates were the main sources of strength, and hydration products were interwoven to form a dense structure with crystals as the framework and gels as fillers.

OPTIMIZATION OF RISERBASE GAS INJECTION FOR SLUG FLOW ATTENUATION

A new approach for the optimization of riserbase gas injection for slug flow attenuation has been proposed. Riserbase gas injection is an established method for slug flow mitigation, however it can be expensive due to the high volume of gas required and the cost of compression. In this study, optimum gas volumes required to stabilise a range of unstable slug flow conditions were obtained using bifurcation maps. The results showed that at the bifurcation point, minimum gas injection volume is required to achieve flow stability. This study established that the optimum gas volume required is dependent on the type of slug flow. For a very high frequency slug flow at high flow rate more volume of gas up to 100kg/s is required to achieve stability while slug flow at moderate flow rate could need up to 30kg/s and slug at low flow rate required about 6 kg/s to achieve stability. The developed approach in this work can help reduce the overall cost of gas injection for slug flow mitigation. Keywords: Slug attenuation; Bifurcation; Gas injection; slug flow; multiphase flow.

Optimisation of mechanical properties of polyethylene terephthalate fibre/fly ash hybrid concrete composite

The study focuses on the prediction and optimisation using modelling with respect to the fresh and hardened properties of polyethylene terephthalate (PET) fibre reinforced concrete containing partial cement replacement with fly ash. Full factorial experimental design methodology was employed to fabricate the test specimens by simultaneously varying the independent factors to develop a model for overall response variation. Numerical optimisation was carried out concerning the fibre reinforced concrete's fresh and hardened mechanical properties. Predictive modified quadratic equations were developed for slump value, compressive, flexural, split tensile strength and total cost. Analysis of variance test was carried out for all the responses indicated and the developed model could predict the slump value and mechanical properties of the fibre reinforced concrete correctly and effectively with a coefficient of determination in the range of 0.5–0.9467. The optimum constituent combination for maximum mechanical strength at the lowest possible cost was found to be 15.76 % fly ash and 0.32 % PET fibre. These optimum values corresponded to responses of 25.65 MPa, 3.69 MPa, 2.36 MPa, 31.48 mm, R2744.17 for compressive strength, flexural strength, tensile strength, slump value and total cost, respectively. These predictions were validated experimentally, and a good correlation was observed between the actual and predicted values based on the observed standard deviations of 0.1335, 0.031, 0.005, 0.676, 0.02 for compressive strength, flexural strength, tensile strength, slump value and cost, respectively. Concrete slabs were optimised for various possible end uses, and the optimum PET fibre % and fly ash % were ascertained. The optimum combination for suspended slabs was 19.09 % for fly ash and 0.34 % PET fibre. These values corresponded to responses of R2742.03/kg/m3, 2.30 MPa, 3.68 MPa, 24.77 MPa, 30.60 mm for the total cost, split tensile, flexural, compressive strength and slump value. For foundation slabs, the optimum combination was 3.94 % fly ash and 0.65 % PET fibre, and the corresponding response values are R 2760.47 /kg/m3, 1.82 MPa, 3.26 MPa, 19.32 MPa and 10.78 mm for a total cost, split tensile, flexural, compressive strength and slump value, respectively. For paving slabs, the optimum combination was 0.65 % PET fibre giving a response of R 2775.13 kg/m3, 1.41 MPa, 3.29 MPa, 19.11 MPa and 9.92 mm for total cost, split tensile, flexural, compressive strength and slump value, respectively.

Comparative analysis of hydrogen production technologies: Hydrothermal oxidation of the "carbonless" aluminum and water electrolysis

The paper deals with the technical and economic comparison of methods of hydrogen production by means of water electrolysis and hydrothermal oxidation of aluminum. Technological chains required for the realization of these methods are analyzed, costs of equipment and maintenance are evaluated. It is demonstrated that for the large-scale production of hydrogen aluminum-water technology is competitive with electrolysis option under the cost of electricity up to 0.02 USD/kWh. The conditions of the maximal feasibility of hydrogen generation using aluminum are specified. Metal hydride thermal sorption compressor is proved to be the best device to commercialize the generated hydrogen. Its application lowers the cost of compression 5–10 times.

Optimal network compression

This paper introduces a formulation of the optimal network compression problem for financial systems. This general formulation is presented for different levels of network compression or rerouting allowed from the initial interbank network. We prove that this problem is, generically, NP-hard. We focus on objective functions generated by systemic risk measures under shocks to the financial network. We use this framework to study the (sub)optimality of the maximally compressed network. We conclude by studying the optimal compression problem for specific networks; this permits us to study, e.g., the so-called robust fragility of certain network topologies more generally as well as the potential benefits and costs of network compression. In particular, under systematic shocks and heterogeneous financial networks the robust fragility results of Acemoglu, Ozdaglar, and Tahbaz-Salehi (2015) no longer hold generally.

The effects of metakaolin on mortar compressive strenght a case study of mortar estrich plester

Mortar as a binding material in couple and stucco work has long been known ranging from very simple technologies to more advanced ones. Nowadays mortar technology has developed so rapidly along with the advancement of construction technology. The development of technology in the construction industry has resulted in better product and system innovations so that they are more competitive and applicable. The demands of increasingly complex needs also need to be responded to wisely and made as hopes and opportunities in business development. Ready-mix mortar is perfect for all kinds of work such as normal masonry, light brick, stucco, ceramics, and floor coating. While from the mechanical properties, the compressive strength of the mortar can meet requirements of standard specifications according to the purpose of its use. Ready-made Dry Plaster Mortar is a mixture of fine aggregate with binding material and various additives. The purpose of using additives is to improve the properties of ready-mix plaster dry mortar. One of the additives used is metakaolin. This study aims to determine the effect of metakaolin on compressive strength and cost efficiency of plastering (mortar). The compressive pressure test object measures 50 mm x 50 mm x 50 mm. Compressive strength testing is carried out at the time when the mortar is 7, 14 and 28 days old. The study was conducted with variations in the use of Metakaolin in ostrich mortar plaster products, namely 0%, 5%, 7.5%, 10%, The results showed that a mixture of ready-made plaster dry mortar with the use of methionine 10% of the weight of cement was able to provide a ready-made dry plaster mortar that meet the requirements in ASTM C 91, Standard specification for masonry cement.

Development and Optimization of Geopolymers Made with Desert Dune Sand and Blast Furnace Slag

This study assesses the effect of mix design parameters on the fresh and hardened properties, cost, and carbon footprint of geopolymer mortar made with desert dune fines (DDF) and blast furnace slag (BFS). Taguchi method was employed in designing the experiments. Four factors were considered, each having three levels, leading to a total of nine geopolymer mortar mixes. The factors comprised the DDF replacement percentage, alkali-activator solution to binder ratio (AAS/B), sodium silicate-to-sodium hydroxide ratio (SS/SH), and sodium hydroxide (SH) molarity. Ten performance criteria were evaluated, including the flowability, final setting time, hardened density, 1, 7, and 28-day compressive strengths, water absorption, sorptivity, cost, and carbon footprint. ANOVA was carried out to estimate the contribution of each factor towards the response criteria. Further, TOPSIS analysis was utilized to optimize the mixture proportions of DDF-BFS blended geopolymer mortar. Experimental results showed that up to 25% DDF replacement enhanced the density, strength, and durability of the geopolymers with minor impact on the flowability and setting time. Higher replacement percentages had a detrimental impact on the performance but could still be utilized in specific mortar construction applications. The other factors had more limited contributions to the performance, evidenced by the ANOVA. TOPSIS method revealed the optimum mix to be made with DDF replacement of 25%, AAS/B of 0.5, SS/SH of 1.5, and SH molarity of 10 M. Different multivariable regression models were also developed to predict the fresh and hardened properties of the DDF-BFS geopolymer mortars using the mix design parameters.

Theoretical Estimation of CO2 Compression and Transport Costs for an hypothetical Carbon Capture & Storage requalification of the Saline Joniche Power Plant Project

SEI S.p.a. presented a project to build a 1320 MW coal-fired power plant in Saline Joniche, on the Southern tip of Calabria Region, Italy, in 2008. A gross early evaluation about the possibility to add CCS (CO2 Capture & Storage) was performed too. The project generated widespread opposition among environmental associations, citizens and local institutions in that period, against the coal use to produce energy, as a consequence of its GHG clima-alterating impact. Moreover the CCS (also named Carbon Capture & Storage or more recently CCUS: Carbon Capture-Usage-Storage) technology was at that time still an unknown and “mysterious” solution for the GHG avoiding to the atmosphere. The present study concerns the sizing of the compression and transportation system of the CCS section, included in the project presented at the time by SEI Spa; the sizing of the compression station and the pipeline connecting the plant to the possible Fosca01 offshore injection site previously studied as a possible storage solution, as part of a coarse screening of CO2 storage sites in the Calabria Region. This study takes into account the costs of construction, operation and maintenance (O&M) of both the compression plant and the sound pipeline, considering the gross static storage capacity of the Fosca01 reservoir as a whole as previously evaluated.

Optimization of the Oxidative Coupling of Methane Process for Ethylene Production

The oxidative coupling of methane (OCM) process is considered an intriguing route for the production of ethylene, one of the most demanded petrochemical products on the market. Ethylene can be produced by various methods, but the most widely used is the steam cracking process. However, due to the current instability of the crude oil market and the shale gas revolution, the production of olefins from natural gas has opened a new path for companies to mitigate the high demand for crude oil while utilizing an abundant amount of natural gas. In this work, the OCM process was compared with other existing processes, and the process was simulated using Aspen HYSYS. The flowsheet was divided into four sections, namely (i) the reaction section, (ii) the water removal section, (iii) the carbon dioxide capture section, and (iv) the ethylene purification section. Each section was thoroughly discussed, and the heat integration of the process was performed to ensure maximum energy utilization. The heat exchanger network was constructed, and the results show that the heating utility can be reduced by more than 95% (from 76567 kW to 2107.5 kW) and the cooling utility can be reduced by more than 60% (from 116398 kW to 41939.2 kW) at an optimum minimum temperature difference of 25 °C. In addition, a case study on the recovery of the high exothermic heat of reaction for power production shows that 16.68 MW can be produced through the cycle, which can cover the total cost of compression.

Cement-based concrete modified with Vitellaria Paradoxa ash: A lifecycle assessment

Building sustainable concrete requires an increasing demand for technology, innovation, and alternative binders to cement. The building sector is technologically driven toward sustainable construction materials and their relationship with the environment. Thus, this study designed three grades of cement-based concrete strengths (C 25, C 30, and C 40) modified with an alternative binder, shea nutshell ash (Vitellaria Paradoxa Ash, VPA). The binder (VPA) was varied at 0–20 wt% of Portland limestone cement (PLC) cured at 28 days, examining the compressive strength cost attained sustainability. Moreover, the embodied energy (EE), global warming potential (GWP) and global temperature potential (GTP) of the concrete compositions were evaluated using the inventory of carbon and energy (ICE) method within the confine of cradle-to-site. Also, the sustainability index (Si) and economic index (Ei) of the concrete mixes were assessed. The results revealed that VPA-cement-based concrete yielded a lesser EE, GWP, GTP, Si, and Eci than the control concrete (Portland limestone cement concrete, PLCC), indicating VPA-cement-based concrete is more sustainable than PLCC. Notwithstanding, an optimum replacement of 15 wt% PLC with VPA is recommended to satisfy all assessments earlier stated for all concrete strength grades. Therefore, these findings can be beneficial in attaining a cleaner built environment and sustainable production. Finally, VPA has proved to be a sustainable building material.

A novel mathematical model for integrating the hydrogen network of refinery with compressor allocation considered

The allocation and cost of compressors have significant influence on hydrogen network. A novel mixed integer nonlinear programming method is proposed for optimizing hydrogen network with the allocation of compressors considered. This model considers the streams compressed stage by stage with multiple compressors and all possible compression paths. The compression power cost of multiple compressors is deduced to optimize the number of compressors in each compression process. The trade-off between the power loss and capital cost of compression is analyzed for different compression paths. The superstructure and mathematical model are built to optimize the hydrogen network in terms of minimizing the total annual cost. The proposed model is flexible and efficient. Three literature cases are studied by the proposed method, and the optimal flowsheets are identified. Compared with previous methods, the computing time is significantly reduced and the total cost of compressors is reduced by 3.38%–8.46%.

Large-scale CO2 transport and storage infrastructure development and cost estimation in the Netherlands offshore

A plan was developed for large-scale transport and storage of CO2, inspired by the measures in The Netherlands Climate Agreement to reduce greenhouse gas emissions to the atmosphere. The main focus was on reduction of CO2 emissions captured from large industrial sources in the Rotterdam harbour area (Rijnmond region). CO2 storage potential is available within depleted gas fields in the Dutch sector of the North Sea. Specific attention was given to the potential for re-use of existing oil and gas infrastructure and the costs and development time of the re-used or new build infrastructure for CO2 transport and storage.The study revealed that depleted gas fields in The Netherlands offshore provide ample storage capacity to accommodate a supply of 10 million tonnes (Mt) CO2 per year by 2030 and for a subsequent period of 40 years. An average total unit technical costs for compression, transport and storage was calculated at €8.6 per tonne CO2. Concurrent operation of four to five reservoirs will be needed if the required 5 Mt annual injection rate in the base case scenario is to be met and eight to nine reservoirs need to be in operation simultaneously with a target rate of 10 Mt per year. In the accelerated case of injection of 10 Mt per year individual reservoirs will be brought on-stream much earlier than in the base case scenario. This can be up to several decades earlier for the reservoirs deployed in the final phase of CO2 storage activities.

Multi-objective optimisation for mortar containing activated waste glass powder

Waste glass is inert and non-degradable which leads to enormous environmental and sustainability troubles, but it can be reused in concrete due to the potential of the pozzolanic activity. This study proposes methods on activity excitation of waste glass powder (WGP) including mechanical, chemical, and mechanical-chemical activation. The results showed that the mortar containing 30% 75 μm WGP activated by the mechanical-chemical method was optimal to increase the mechanical property and reduce the detrimental expansion. In addition, the microstructural analysis was conducted to explore the activation effect on WGP and WGP-cement system. An artificial intelligence (AI) based multi-objective optimisation (MOO) model was proposed to seek the optimal mix proportions for the unconfined compression strength (UCS), alkali-silica reaction (ASR), and cost. A comprehensive dataset was investigated including 549 specimens for the UCS test and 366 test results for the expansion test. Random Forest (RF) model was utilized for the prediction of UCS and ASR values with hyperparameters tuned by a firefly algorithm (FA). The high correlation coefficients (0.93 for UCS and 0.91 for ASR) verified the feasibility of FA-RF. Subsequently, the FA-RF model was extended as the objective function for the mi-objective firefly algorithm (MOFA-RF) to obtain the consequent Pareto fronts. This paper combined the results of experiments, machine learning prediction, and multi-objective optimisation design for activated WGP mortar, which provided a comprehensive basis for the practical application.

Optimisation and Prediction of Fresh Ultra-High-Performance Concrete Properties Enhanced with Nanosilica

The use of high chemical admixture dosages in ultra-high-performance concrete (UHPC) mixtures to achieve adequate water demand can slow down early cement hydration and prolong the setting time. In this study, the effects of nanosilica (Ns) with high chemical admixture dosages on the rheological properties of UHPC was investigated. A factorial design approach was employed to predict and optimise the Ns content, water-binder ratio (W/B), and sand-binder (s/b) ratio to obtain the best flowability, setting time, and compressive strength. This study represents an attempt to modelling and optimise eighteen UHPC mixtures containing various proportions of water, cement, and sand, with the Ns powder as a possible property enhancer to achieve the best rheological properties. Response surface analyses revealed the significant effect of Ns in controlling the prolonged setting time and improving the compressive strength. Based on the applied criterion conditions, the optimisation results indicated two mixtures targeting either the maximum compressive strength or cost effective materials. The use of a 1.12 s/b ratio with a controlling level of 0.8% Ns content was suitable to fulfil the compressive strength, flow, and setting time limit values.

Pressurized Formic Acid Dehydrogenation: An Entropic Spring Replaces Hydrogen Compression Cost.

Formic acid is unique among liquid organic hydrogen carriers (LOHCs), because its dehydrogenation is highly entropically driven. This enables the evolution of high-pressure hydrogen at mild temperatures that is difficult to achieve with other LOHCs, conceptually by releasing the "spring" of energy stored entropically in the liquid carrier. Applications calling for hydrogen-on-demand, such as vehicle filling, require pressurized H2. Hydrogen compression dominates the cost for such applications, yet there are very few reports of selective, catalytic dehydrogenation of formic acid at elevated pressure. Herein, we show that homogenous catalysts with various ligand frameworks, including Noyori-type tridentate (PNP, SNS, SNP, SNPO), bidentate chelates (pyridyl)NHC, (pyridyl)phosphine, (pyridyl)sulfonamide, and their metallic precursors, are suitable catalysts for the dehydrogenation of neat formic acid under self-pressurizing conditions. Quite surprisingly, we discovered that their structural differences can be related to performance differences in their respective structural families, with some tolerant or intolerant of pressure and others that are significantly advantaged by pressurized conditions. We further find important roles for H2 and CO in catalyst activation and speciation. In fact, for certain systems, CO behaves as a healing reagent when trapped in a pressurizing reactor system, enabling extended life from systems that would be otherwise deactivated.

Innovative combined optimization and modified maximum rectangle method for equipment sizing and operational strategy of an integrated system with cold thermal storage

An innovative method is proposed here for optimum sizing of an integrated system and finding its operational strategy of equipment during a year. This system provided power, heating, and cooling loads of buildings. To decrease the electricity consumption and operating cost of compression cooling system, an ice thermal energy storage (ITES) and also absorption chiller included in the integrated system. Modified Maximum Rectangle Method (MRM M) is defined and combined with multi-objective optimization technique. Two objective functions were Relative Annual Benefit (RAB) and Exergy Efficiency (ηEx,tot). For a residential complex, MRMM and GA optimization methods obtained results in a more accurate and faster procedure. Analysis of results from OPT-MRMM showed that two 884 kW gas engines provided the highest exergy efficiency (46.54%), the maximum value of RAB (1.04 × 106 $/year), and the shortest payback period (3.64 years) for the optimized and selected integrated system in comparison with system specifications obtained by other studied methods. Results also showed that OPT-MRMM method provided the lowest waste heat, the lowest fuel consumption in backup boilers, the highest amount of selling electricity to the grid and the lowest amount of specific emission release in comparison with those for optimization or MRM method alone. Applying this method provided low amount of buying electricity from the grid as well.The results for our case study also showed that the annual electricity consumption of traditional Vapor Compression Refrigeration (VCR) reduced from 19.99 × 105 kWh/year to 16.18 × 105 kWh/year (3.81 × 105 kWh/year reduction i.e., 19%) when ITES added to the VCR equipment. Furthermore, shifting the electricity consumption from high tariff period (on-peak and mid-peak hours) to low tariff period (off-peak hours), reduced the annual electricity cost for 26.62%. Finally, the results showed 25%–32% reduction for annual electricity consumption of VCR-ITES in OPT-MRMM method in comparison with that for VCR alone.

Techno-Economics Optimization of H2 and CO2 Compression for Renewable Energy Storage and Power-to-Gas Applications

The decarbonization of the industrial sector is imperative to achieve a sustainable future. Carbon capture and storage technologies are the leading options, but lately the use of CO2 is also being considered as a very attractive alternative that approaches a circular economy. In this regard, power to gas is a promising option to take advantage of renewable H2 by converting it, together with the captured CO2, into renewable gases, in particular renewable methane. As renewable energy production, or the mismatch between renewable production and consumption, is not constant, it is essential to store renewable H2 or CO2 to properly run a methanation installation and produce renewable gas. This work analyses and optimizes the system layout and storage pressure and presents an annual cost (including CAPEX and OPEX) minimization. Results show the proper compression stages need to achieve the storage pressure that minimizes the system cost. This pressure is just below the supercritical pressure for CO2 and at lower pressures for H2, around 67 bar. This last quantity is in agreement with the usual pressures to store and distribute natural gas. Moreover, the H2 storage costs are higher than that of CO2, even with lower mass quantities; this is due to the lower H2 density compared with CO2. Finally, it is concluded that the compressor costs are the most relevant costs for CO2 compression, but the storage tank costs are the most relevant in the case of H2.

Application of the ITS-UCD Model for the Assessment of CO2 Compression and Transport Costs for the Simeri Crichi - Botricello1 Route in a Theoretical CCS Retrofit Project of the Simeri Crichi Thermal Power Plant

The power plant of Simeri Crichi (Calabria Region, Italy) under study was already managed by Edison S.p.A. and it is fueled by natural gas. This study is dealing with the hypothesis to perform a retrofit device of the plant, with the addition of a standard “CO2 Capture”, able to perform a capture rate up to 90%; it has been proposed here the sizing of the compression station and the pipeline which connects the plant to the injection site Botricello 1, studied in the frame of a gross screening of the storage sites in the Calabria Region in Italy. This study took into account the costs of construction, operation and maintenance (O&M) of both the compression plant and the sound pipeline. Eventually, an estimation of the gross static storage capacity of the Botricello1 reservoir is provided.

Sustainable Gas-to-Wire via dry reforming of carbonated natural gas: Ionic-liquid pre-combustion capture and thermodynamic efficiency

Remotely located oil fields with high gas-oil ratio and high carbon dioxide content impose challenges for efficient and sustainable gas processing and monetization. This work investigates gas-to-wire coupled to carbon dioxide enhanced oil recovery as a solution to handle the high flow of carbonated natural gas simultaneously accomplishing three missions: high revenues from electricity exportation; and elimination of concerns from long-distance gas transportation and carbon dioxide destination. A novel Gas-to-Wire concept is proposed matching the low-emission target tied to high carbon dioxide intake with a pre-combustion strategy using dry reforming of carbonated gas followed by ionic-liquid absorption carbon capture coupled to high-pressure stripping to lower carbon dioxide compression costs. The novel process is thermodynamically, environmentally and economically compared to an analogous Gas-to-Wire using conventional aqueous-monoethanolamine absorption capture and low-pressure stripping. Results show that the ionic-liquid Gas-to-Wire has cumulatively the following advantages over the aqueous-monoethanolamine counterpart: (i) higher overall thermodynamic efficiency of 23.5% against 16.3%; (ii) lower heat-penalty due to lower stripping heat-ratio; (iii) 7.8% lower power demand due to lower carbon dioxide compression power; and (iv) 60.4% higher net value due to 41.7% greater electricity exportation demanding only 5.3% higher investment due to smaller carbon dioxide compression train.