CO2 emissions from Polish cement industry

The cement industry is one of the most significant sources of anthropogenic emissions of CO₂. It is connected with the specific character of the production processes, during which great quantities of CO₂ are produced. Basic actions to reduce CO₂ emissions recommended by the European Union's, Reference Document on Best Available Techniques in the Cement and Lime Manufacturing Industries, include: reduction of fuel consumption, selection of raw materials with low content of organic compounds and fuels with low coal contribution to heating value. All actions connected with the improvement of energy conversion efficiency of the cement production process cause CO₂ emissions reduction. The use of at most acceptable by the valid standards amounts of waste as raw materials and additives for cement production, also brings about the reduction of significant part of CO₂ emissions. These measures have been and continue to be pursued by the cement factories in Poland. This article describes the evolution of the cement industry in Poland over the period 1998–2008 and the resulting changes in CO₂ emissions and explores the drivers for these changes. The sources of CO₂ emissions in cement industry have been presented in this article as well as a discussion of potential ways to reduce Polish cement industry emissions even further.     

Carbonation of brine impacted fractionated coal fly ash: implications for CO2 sequestration

Coal combustion by-products such as fly ash (FA), brine and CO(2) from coal fired power plants have the potential to impact negatively on the environment. FA and brine can contaminate the soil, surface and ground water through leaching of toxic elements present in their matrices while CO(2) has been identified as a green house gas that contributes significantly towards the global warming effect. Reaction of CO(2) with FA/brine slurry can potentially provide a viable route for CO(2) sequestration via formation of mineral carbonates. Fractionated FA has varying amounts of CaO which not only increases the brine pH but can also be converted into an environmentally benign calcite. Carbonation efficiency of fractionated and brine impacted FA was investigated in this study. Controlled carbonation reactions were carried out in a reactor set-up to evaluate the effect of fractionation on the carbonation efficiency of FA. Chemical and mineralogical characteristics of fresh and carbonated ash were evaluated using XRF, SEM, and XRD. Brine effluents were characterized using ICP-MS and IC. A factorial experimental approach was employed in testing the variables. The 20-150 μm size fraction was observed to have the highest CO(2) sequestration potential of 71.84 kg of CO(2) per ton of FA while the >150 μm particles had the lowest potential of 36.47 kg of CO(2) per ton of FA. Carbonation using brine resulted in higher degree of calcite formation compared to the ultra-pure water carbonated residues.     

Application of a system dynamics approach for assessment and mitigation of CO2 emissions from the cement industry

A system dynamics model based on the dynamic interactions among a number of system components is developed to estimate CO(2) emissions from the cement industry in India. The CO(2) emissions are projected to reach 396.89 million tonnes by the year 2020 if the existing cement making technological options are followed. Policy options of population growth stabilisation, energy conservation and structural management in cement manufacturing processes are incorporated for developing the CO(2) mitigation scenarios. A 42% reduction in the CO(2) emissions can be achieved in the year 2020 based on an integrated mitigation scenario. Indirect CO(2) emissions from the transport of raw materials to the cement plants and finished product to market are also estimated.     

A solution against well cement degradation under CO2 geological storage environment

Capturing and storing carbon dioxide (CO₂) underground for thousands of years is one way to reduce atmospheric greenhouse gases, often associated with global warming. Leakage through wells is one of the major issues when storing CO₂ in depleted oil or gas reservoirs. CO₂-injection candidates may be new wells, or old wells that are active, closed or abandoned. In all cases, it is critical to ensure that the long-term integrity of the storage wells is not compromised. The loss of well integrity may often be explained by the geochemical alteration of hydrated cement that is used to isolate the annulus across the producing/injection intervals in CO₂-related wells. However, even before any chemical degradation, changes in downhole conditions due to supercritical CO₂ injections can also be responsible for cement debonding from the casing and/or from the formation, leading to rapid CO₂ leakage. A new cement with better CO₂ resistance is compared with conventional cement using experimental procedure and methodology simulating the interaction of set cement with injected, supercritical CO₂ under downhole conditions. Geochemical experimental data and a mechanical modeling approach are presented. The use of adding expanding property to this new cement to avoid microannulus development during the CO₂ injection is discussed.     

Rate modeling of CO2 stripping from potassium carbonate promoted by piperazine

This work presents results from a rate-based model of strippers at normal pressure (160 kPa) and vacuum (30 kPa) in Aspen Custom Modeler^® (ACM) for the desorption of CO₂ from 5 m K⁺/2.5 m piperazine (PZ). The model solves the material, equilibrium, summation and enthalpy (MESH) equations, the heat and mass transfer rate equations, and computes the reboiler duty and equivalent work for the stripping process. Simulations were performed with IMTP #40 random packing and a temperature approach on the hot side of the cross-exchanger of 5 °C and 10 °C. A “short and fat” stripper requires 7–15% less total equivalent work than a “tall and skinny” one because of the reduced pressure drop. The vacuum and normal pressure strippers require 230 s and 115 s of liquid retention time to get an equivalent work 4% greater than the minimum work. Stripping at 30 kPa was controlled by mass transfer with reaction in the boundary layer and diffusion of reactants and products (88% resistance at the rich end and 71% resistance at the lean end). Stripping at 160 kPa was controlled by mass transfer with equilibrium reactions (84% resistance at the rich end and 74% resistance at the lean end) at 80% flood. The typical predicted energy requirement for stripping and compression to 10 MPa to achieve 90% CO₂ removal was 37 kJ/gmol CO₂. This is about 25% of the net output of a 500 MW power plant with 90% CO₂ removal.     

Analysis and performance of oil well cement with 30 years of CO2 exposure from the SACROC Unit,West Texas,USA

A core sample including casing, cement, and shale caprock was obtained from a 30-year old CO₂-flooding operation at the SACROC Unit, located in West Texas. The core was investigated as part of a program to evaluate the integrity of Portland-cement based wellbore systems in CO₂-sequestration environments. The recovered cement had air permeabilities in the tenth of a milliDarcy range and thus retained its capacity to prevent significant flow of CO₂. There was evidence, however, for CO₂ migration along both the casing–cement and cement–shale interfaces. A 0.1–0.3 cm thick carbonate precipitate occurs adjacent to the casing. The CO₂ producing this deposit may have traveled up the casing wall or may have infiltrated through the casing threads or points of corrosion. The cement in contact with the shale (0.1–1 cm thick) was heavily carbonated to an assemblage of calcite, aragonite, vaterite, and amorphous alumino-silica residue and was transformed to a distinctive orange color. The CO₂ causing this reaction originated by migration along the cement–shale interface where the presence of shale fragments (filter cake) may have provided a fluid pathway. The integrity of the casing–cement and cement–shale interfaces appears to be the most important issue in the performance of wellbore systems in a CO₂ sequestration reservoir.     

An experimental and numerical investigation into the impact of dissolution/precipitation mechanisms on CO2 injectivity in the wellbore and far field regions

Carbon dioxide capture and storage (CCS) technology is gaining credibility as the best short to medium term solution for significantly reducing net carbon emissions into the atmosphere. From a capacity point of view, deep saline aquifers offer the greatest potential for CO₂ storage. In this respect, well injectivity is considered a key technical and economical issue. Rock/fluid interactions – dissolution/precipitation of minerals, in particular carbonates – are currently considered as one of the principal reasons for wellbore injectivity changes in aquifers.This research investigated the mechanisms involved in injectivity losses through experimental and theoretical methods. The impact on injectivity of permeability changes occurring at various distances from the wellbore was studied using an idealised CO₂ injection well flow model. A new experimental set-up was used to investigate the effect on dissolution/precipitation mechanisms of the pressure and temperature changes that the fluid is subjected to as it advances from the wellbore.Numerical modelling of the injection wellbore has shown that changes in the petrophysical properties of the reservoir several metres away from the wellbore can still have a significant impact on injectivity. As indicated by the experimental research carried out, pressure and temperature gradients that exist inside the reservoirs may lead to re-precipitation in the far field, however no significant permeability and porosity changes were detected to suggest major losses of injectivity due to these effects.     

Numerical simulation on multi-scale diffusion of CO2 injected in the deep ocean in a practical scenario

The direct injection of CO₂ into the deep ocean is one of the ways for the mitigation of the global warming. There is, however, a concern about its environmental impact near the injection point. To minimize its biological impact, it is necessary to make CO₂ disperse as fast as possible and it is thought that injection with pipes towed by moving-ships is effective for this purpose. Because the injection ships are planned to move in the site, the order of magnitude of which is 10² km, a mesoscale model is required to predict CO₂ fate in seawater. At the same time, it is required to predict the concentration precisely near the injection points, which move with the ships in the mesoscale domain. In this study, a multi-scale ocean model was developed to analyze the dispersion of CO₂ in the deep ocean: the model consists of a fixed mesoscale domain and 5 small-scale domains nesting in the mesoscale domain. Each small-scale domain involves 6 pipes and moves along with the trajectories of the injection ships. From the results of the present numerical simulation, the developed technique demonstrated its applicability as a tool to optimise the system to dilute CO₂ below some criterion of biological impact.     

CO2 recycling by reaction with renewably-generated hydrogen

A laboratory-scale reactor system was built and operated to demonstrate the feasibility of catalytically reacting carbon dioxide (CO₂) with renewably-generated hydrogen (H₂) to produce methane (CH₄) according to the Sabatier reaction: CO₂ + 4H₂ → CH₄ + 2H₂O. A cylindrical reaction vessel packed with a commercial methanation catalyst (Haldor Topsøe PK-7R) was used. Renewable H₂ produced by electrolysis of water (from solar- and wind-generated electricity) was fed into the reactor along with a custom blend of 2% CO₂ in N₂, meant to represent a synthetic exhaust mixture. Reaction conditions of temperature, flow rates, and gas mixing ratios were varied to determine optimum performance. The extent of reaction was monitored by real-time measurement of CO₂ and CH₄. Maximum conversion of CO₂ occurred at 300–350 °C. Approximately 60% conversion of CO₂ was realized at a space velocity of about 10,000 h^?1 with a molar ratio of H₂/CO₂ of 4/1. Somewhat higher total CO₂ conversion was possible by increasing the H₂/CO₂ ratio, but the most efficient use of available H₂ occurs at a lower H₂/CO₂ ratio.     

Dispersion by wind of CO2 leaking from underground storage: Comparison of analytical solution with simulation

The concentration of CO₂ in air near the ground needs to be predicted to assess environmental and health risks from leaking underground storage. There is an exact solution to the advection–diffusion equation describing trace gases carried by wind when the wind profile is modeled with a power-law dependence on height. The analytical solution is compared with a numerical simulation of the coupled air–ground system with a source of CO₂ underground at the water table. The two methods produce similar results far from the boundaries, but the boundary conditions have a strong effect; the simulation imposes boundary conditions at the edge of a finite domain while the analytic solution imposes them at infinity. The reverse seepage from air to ground is shown in the simulation to be very small, and the large difference between time scales suggests that air and ground can be modeled separately, with gas emissions from the ground model used as inputs to the air model.     

Prospects for cost-effective post-combustion CO2 capture from industrial CHPs

Industrial Combined Heat and Power plants (CHPs) are often operated at partial load conditions. If CO₂ is captured from a CHP, additional energy requirements can be fully or partly met by increasing the load. Load increase improves plant efficiency and, consequently, part of the additional energy consumption would be offset. If this advantage is large enough, industrial CHPs may become an attractive option for CO₂ capture and storage CCS. We therefore investigated the techno-economic performance of post-combustion CO₂ capture from small-to-medium-scale (50–200 MWe maximum electrical capacity) industrial Natural Gas Combined Cycle- (NGCC-) CHPs in comparison with large-scale (400 MWe) NGCCs in the short term (2010) and the mid-term future (2020–2025). The analyzed system encompasses NGCC, CO₂ capture, compression, and branch CO₂ pipeline.The technical results showed that CO₂ capture energy requirement for industrial NGCC-CHPs is significantly lower than that for 400 MWe NGCCs: up to 16% in the short term and up to 12% in the mid-term future. The economic results showed that at low heat-to-power ratio operations, CO₂ capture from industrial NGCC-CHPs at 100 MWe in the short term (41–44 €/tCO₂ avoided) and 200 MWe in the mid-term future (33–36 €/tCO₂ avoided) may compete with 400 MWe NGCCs (46–50 €/tCO₂ avoided short term, 30–35 €/tCO₂ avoided mid-term).     

Energy and CO2 from high performance recycled aggregate production

The use of recycled concrete aggregates (RCA) in applications other than road sub-layers is limited by two factors: the high porosity of RCA in comparison with natural aggregates, and the restrictions set forth in standards and building codes. Research efforts aimed at alleviating these restrictions are focused on improving the quality of coarse RCAs by reducing the amount of adhered cement pastes, which is the weakest element in this system and influences the rheological behaviour.This paper presents an analysis of the environmental impacts of the recent mechanical and thermo-mechanical processing techniques which produce high performance RCA by reducing the volume of adhered cement paste. Based on published data, processing scenarios were established. These scenarios permit making rough estimates of energy consumption, CO₂ emissions, fines generation and product quality. Using these data and the available emission factors from several countries, an objective comparison was made between these innovating processes and conventional recycling.The production of fines increases from 40% up to as much as 70% as the volume of adhered cement paste on the RCA is reduced. Fuel fed thermo-mechanical process energy consumption, per tonne of recycled aggregate, varies between 36 and 62 times higher than conventional recycling processes. Mechanical processing, combined with microwave heating, increases energy consumption from 3 to a little more than 4 times conventional recycling. Consequently, CO₂ emissions released by conventional coarse aggregate production go from 1.5 to 4.5 kgCO₂/t, to around 200 kgCO₂/t, for that of fossil fuel fed thermo-mechanical treatments.Mechanical and mechanical/microwave treatments appear to have the greatest environmental potential. Notwithstanding, the further development of markets for fines is crucial for reducing environmental loads.     

Short-Term Opportunities for Decreasing CO2 Emissions from the Steel Industry

There is a strong political will to decrease CO₂ emissions. Although the steel industry only accounts for some 5% of worldwide CO₂ emissions (which totalled 1,200 million tonnes per annum in the late 1990s), it will be strongly affected by this. The EU, for example, is putting up strong economic incentives for reductions. This is taking place at a time when demand for steel products is greater than ever. To radically change existing processes and production routes to decrease the CO₂ emissions would be extremely expensive, even if it were possible. Nevertheless, many of the solutions which have been discussed seem to go in this direction. The other alternative discussed seems to be the creation of process solutions and alterations that lead to a focusing of CO₂ streams, i.e., much higher CO₂ concentrations in flue gases than today, for entrapment of the CO₂ so that it is not discharged into the atmosphere. These solutions are feasible, but expensive.

However, there exists today a number of solutions and technologies which, if fully implemented, could substantially decrease CO₂ emissions without seriously altering current methods of operation; they are short-term viable solutions. The present paper reviews and discusses such technologies, throughout the steel production paths. If these solutions are fully implemented, the combined impact on CO₂ emissions from the steel industry worldwide is estimated to be a reduction of 100–150 million tonnes of CO₂ per annum, i.e., current emissions can be reduced by some 8–10% within a relatively short time span.     

CO2 capture from hot stove gas in steel making process

The capture of CO₂ from a hot stove gas in steel making process containing 30 vol% CO₂ by chemical absorption in a rotating packed bed (RPB) was studied. The RPB had an inner diameter of 7.6 cm, an outer diameter of 16 cm, and a height of 2 cm. The aqueous solutions containing 30 wt% of single and mixed monoethanolamine (MEA), 2-(2-aminoethylamino)ethanol (AEEA), and piperazine (PZ) were used. The CO₂ capture efficiency was found to increase with increasing temperature in a range of 303–333 K. It was also found to be more dependent on gas and liquid flow rates but less dependent on rotating speed when the speed was higher than 700 rpm. The obtained results indicated that the mixed alkanolamine solutions containing PZ were more effective than the single alkanolamine solutions. This was attributed to the highest reaction rate of PZ with CO₂. A higher portion of PZ in the mixture was more favorable to CO₂ capture. The highest gas flow rates allowed to achieve a desired CO₂ capture efficiency and the correspondent height of transfer unit (HTU) were determined at different aqueous solution flow rates. Because all the 30 wt% single and mixed alkanolamine solutions could result in a HTU less than 5.0 cm at a liquid flow rate of 100 mL/min, chemical absorption in a RPB instead of a packed bed adsorber is therefore suggested to capture CO₂ from the flue gases in steel making processes.     

Techno-economic study of CO2 capture from natural gas based hydrogen plants

Canadian oil sands are considered to be the second largest oil reserves in the world. However, the upgrading of bitumen from oil sands to synthetic crude oil (SCO) requires nearly ten times more hydrogen (H₂) than conventional crude oils. The current H₂ demand for oil sands operations is met mostly by steam reforming of natural gas (SMR). The future expansion of oil sands operations is likely to quadruple the demand of H₂ for oil sand operations in the next decade.This paper presents modified process schemes that capture CO₂ at minimum energy penalty in modern SMR plants. The approach is to simulate a base case H₂ plant without CO₂ capture and then look for the best operating conditions that minimize the energy penalty associated with CO₂ capture while maximizing H₂ production. The two CO₂ capture schemes evaluated in this study include a membrane separation process and the monoethanolamine (MEA) absorption process. A low energy penalty is observed when there is lower CO₂ production and higher steam production. The process simulation results show that the H₂ plant with CO₂ capture has to be operated at lower steam to carbon ratio (S/C), higher inlet temperature of the SMR and lower inlet temperatures for the water gas-shift (WGS) converters to attain lowest energy penalty. Also it is observed that both CO₂ capture processes, the membrane process and the MEA absorption process, are comparable in terms of energy penalty and CO₂ avoided when both are operated at conditions where lowest energy penalty exists.     

CO2 mineral sequestration in oil-shale wastes from Estonian power production

In the Republic of Estonia, local low-grade carbonaceous fossil fuel--Estonian oil-shale--is used as a primary energy source. Combustion of oil-shale is characterized by a high specific carbon emission factor (CEF). In Estonia, the power sector is the largest CO(2) emitter and is also a source of huge amounts of waste ash. Oil-shale has been burned by pulverized firing (PF) since 1959 and in circulating fluidized-bed combustors (CFBCs) since 2004-2005. Depending on the combustion technology, the ash contains a total of up to 30% free Ca-Mg oxides. In consequence, some amount of emitted CO(2) is bound by alkaline transportation water and by the ash during hydraulic transportation and open-air deposition. The goal of this study was to investigate the possibility of improving the extent of CO(2) capture using additional chemical and technological means, in particular the treatment of aqueous ash suspensions with model flue gases containing 10-15% CO(2). The results indicated that both types of ash (PF and CFBC) could be used as sorbents for CO(2) mineral sequestration. The amount of CO(2) captured averaged 60-65% of the carbonaceous CO(2) and 10-11% of the total CO(2) emissions.     

CO2 capture by adsorption: Materials and process development

Vacuum swing adsorptive (VSA) capture of CO₂ from flue gas and related process streams is a promising technology for greenhouse gas mitigation. Although early reports suggested that VSA was problematic and expensive, through the application of more logical process configurations that are appropriately coupled to the composition of the feed and product gas streams, we can now refute this early assertion. Improved cycle designs coupled with tighter temperature control are also helping to optimise performance for CO₂ separation. Simultaneously, new adsorbent materials are being developed. These separate CO₂ by selective (acid-base) reaction with surface bound amine groups (chemisorption), rather than on the basis of non-bonding interactions (physisorption). This report describes some of these recent developments from our own laboratories and points to synergies that are anticipated as a result of combining these improvements in adsorbent properties and VSA process cycles.     

Purification of oxyfuel-derived CO2

Oxyfuel combustion in a pulverised fuel coal-fired power station produces a raw CO₂ product containing contaminants such as water vapour plus oxygen, nitrogen and argon derived from the excess oxygen for combustion, impurities in the oxygen used, and any air leakage into the system. There are also acid gases present, such as SO₃, SO₂, HCl and NO_x produced as byproducts of combustion. At GHGT8 (White and Allam, 2006) we presented reactions that gave a path-way for SO₂ to be removed as H₂SO₄ and NO and NO₂ to be removed as HNO₃. In this paper we present initial results from the OxyCoal-UK project in which these reactions are being studied experimentally to provide the important reaction kinetic information that is so far missing from the literature. This experimental work is being carried out at Imperial College London with synthetic flue gas and then using actual flue gas via a sidestream at Doosan Babcock's 160 kW coal-fired oxyfuel rig. The results produced support the theory that SO_x and NO_x components can be removed during compression of raw oxyfuel-derived CO₂ and therefore, for emissions control and CO₂ product purity, traditional FGD and deNO_x systems should not be required in an oxyfuel-fired coal power plant.     

Development and Experimental Study of CO2 Expander in CO2 Supercritical Refrigeration Cycles

Abstract

As one of the natural working fluids for the refrigeration system, CO₂ has been attracting increasing attention over the last ten years. But CO₂ has to work at the supercritical region for the so-called “condensation” process regarding the conventional refrigerants and evaporate at the two-phase region, and therefore results in larger throttling loss for the practical refrigeration application. Consequently, new technologies must be developed to improve the performance efficiency of the CO₂ transcritical cycle, and make it to be equal or closer to that of the refrigeration system with the conventional refrigerants. In this study, an expander is employed in the CO₂ transcritical cycle to replace the throttling valve, and as a result the throttling loss can be decreased significantly. The paper presents the development of a rolling piston expander and the activity items in the expander design, including the seal technology, the contact friction control, the suction design, etc. The performance experiments for the expander are conducted in the present testing system for the CO₂ transcritical cycle. The results show that the recovery power of the expander is related to the revolution speed of the expander. The efficiency of the expander prototype is observed to be about 32%.