Reduction of Greenhouse Gas Emissions from Gas,Oil, and Coal Power Plants in Pakistan by Carbon Capture and Storage (CCS): A Review

The production of energy in Pakistan as a developing country mainly depends on consumption of fossil fuels, which are the main sources of greenhouse gas (GHG) emissions. These emissions can be mitigated by implementing carbon capture and storage (CCS) in running plants. An overview of the current and future potentials of Pakistan for CCS is provided, indicating a great potential for this technology to capture CO₂ emissions. The amine CO₂ capture process as the most mature procedure is currently applied in many oil and gas companies in Pakistan, which can be employed to capture CO₂ from other industries as well. Pakistan has a great CO₂ storage potential in oil, gas, and coal fields and in saline aquifer as well as significant resources of Mg and Ca silicates suitable as feedstock in the carbon mineralization process. For further development and implementation of CCS technologies in Pakistan, economic and policy barriers as the main obstacles should be alleviated.     

煤和焦炉气联供制烯烃过程的建模模拟与分析

由于煤富碳少氢,煤制烯烃过程生产1 t产品将排放约5.8 t CO₂.与此同时,中国焦炭工业每年产生约7×10¹⁰ m³的副产物焦炉气,这些富氢的焦炉气大多被燃烧或直接排放进入大气,对环境造成严重影响的同时还浪费了巨大的经济价值.本文对焦炉气辅助煤制烯烃的新过程进行了建模模拟与系统分析.焦炉气与煤元素互补,焦炉气中的H₂可用来调节合成气的氢碳比;CH₄可通过甲烷水蒸气重整和甲烷干重整两个过程,提高合成气的氢碳比的同时降低煤制烯烃过程排放的CO₂,提高碳元素利用率,实现节能减排.这个新的联供过程的能效比煤制烯烃过程提高了约10个百分点,而CO₂排放量则减少了约95%.     

Combining coal gasification and natural gas reforming for efficient polygeneration

A techno-economic analysis of several process systems to convert coal and natural gas to electricity, methanol, diesel, and gasoline is presented. For these polygeneration systems, a wide range of product portfolios and market conditions are considered, including the implementation of a CO₂ emissions tax policy and optional carbon capture and sequestration technology. A new strategy is proposed in which natural gas reforming is used to cool the gasifier, rather than steam generation. Simulations along with economic analyses show that this strategy provides increased energy efficiency and can be the optimal design choice in many market scenarios.     

煤和焦炉气联供制合成天然气过程的建模、模拟与分析

近年来中国的煤制天然气项目快速发展。然而煤制天然气项目的CO₂排放量大、污水产量高难处理,生产过程能效低。与此同时,中国焦炭工业每年产生约700亿立方米的副产物焦炉气,这些富氢的焦炉气大多被燃烧或直接排放进入大气,对环境造成严重影响,同时还浪费了巨大的经济价值。煤和焦炉气联供制天然气新工艺可有效解决这些问题。焦炉气与煤元素互补,焦炉气中的氢气可用来调节合成气的氢碳比;甲烷可通过甲烷干重整过程降低煤制烯烃过程排放的CO₂,提高碳元素利用率,实现节能减排。本文针对煤和焦炉气联供制天然气这个新的工艺过程进行建模、模拟与分析,发现新过程的能效比煤天然气烃过程提高了约8个百分点,而CO₂排放量则减少了约60%。     

基于化学链燃烧的吸收剂引导的焦炉煤气水蒸气重整制氢过程模拟

建立了基于化学链燃烧供能的吸收剂引导的焦炉煤气水蒸气重整制氢系统，该系统包含吸收剂引导的焦炉煤气重整反应器（SECOGSR）、燃料反应器和空气反应器。该系统能产生高纯H₂［93.23%（mol）］，仅通过冷凝即可实现CO₂的捕获，分离能耗低。采用Aspen Plus软件对吸收剂引导的焦炉煤气重整制氢过程进行了模拟，得到优化的反应条件为：温度650℃，压力1.5 MPa，Ca/C=1，H₂O/C=4。并对系统进行了模拟，以NiO/Y₂O₃/ZrO₂(0.73/0.022/0.248，摩尔比）为化学链燃烧的载氧体和载能体，在满足反应器自热平衡和系统吸放热平衡的基础上，重整1mol焦炉煤气，燃料反应器和空气反应器所需的焦炉煤气、空气及载氧体NiO/Y₂O₃/ZrO₂的量分别为0.139、0.648、3.11 mol。该系统消耗1 mol焦炉煤气的产H₂量为1.30 mol，捕获的CO₂的量为0.355 mol。     

CO2 capture using oxygen enhanced combustion strategies for natural gas power plants

This paper describes a series of experiments conducted with natural gas in air and in mixtures of oxygen and recycled flue gas, termed O₂/CO₂ recycle combustion. The objective is to enrich the flue gas with CO₂ to facilitate its capture and sequestration. Detailed measurements of gas composition, flame temperature and heat flux profiles were taken inside CANMET's 0.3 MWth down-fired vertical combustor fitted with a proprietary pilot scale burner. Flue gas composition was continuously monitored. The effects of burner operation, including swirling of secondary stream and air staging, on flame characteristics and NO_x emissions were also studied. The results of this work indicate that oxy-gas combustion techniques based on O₂/CO₂ combustion with flue gas recycle offer excellent potential for retrofit to conventional boilers for CO₂ emission abatement. Other benefits of the technology include considerable reduction and even elimination of NO_x emissions, improved plant efficiency due to lower gas volume and better operational flexibility.     

Combining coal gasification, natural gas reforming, and solid oxide fuel cells for efficient polygeneration with CO2 capture and sequestration

Several polygeneration process systems are presented which convert natural gas and coal to gasoline, diesel, methanol, and electricity. By using solid oxide fuel cells as the primary electricity generator, the presented systems improve upon a recently introduced concept by which natural gas is reformed inside the radiant cooler of a gasifier. Simulations and techno-economic analyses performed for a wide range of process configurations and market conditions show that this strategy results in significant efficiency and profitability improvements when CO₂ capture and sequestration are employed. Market considerations for this analysis include variations in purchase prices of the coal and natural gas, sale prices of the products, and CO₂ emission tax rates.     

Optimization of energy usage for fleet‐wide power generating system under carbon mitigation options

This article presents a fleet‐wide model for energy planning that can be used to determine the optimal structure necessary to meet a given CO₂ reduction target while maintaining or enhancing power to the grid. The model incorporates power generation as well as CO₂ emissions from a fleet of generating stations (hydroelectric, fossil fuel, nuclear, and wind). The model is formulated as a mixed integer program and is used to optimize an existing fleet as well as recommend new additional generating stations, carbon capture and storage, and retrofit actions to meet a CO₂ reduction target and electricity demand at a minimum overall cost. The model was applied to the energy supply system operated by Ontario power generation (OPG) for the province of Ontario, Canada. In 2002, OPG operated 79 electricity generating stations; 5 are fueled with coal (with a total of 23 boilers), 1 by natural gas (4 boilers), 3 nuclear, 69 hydroelectric and 1 wind turbine generating a total of 115.8 TWh. No CO₂ capture process existed at any OPG power plant; about 36.7 million tonnes of CO₂ was emitted in 2002, mainly from fossil fuel power plants. Four electricity demand scenarios were considered over a span of 10 years and for each case the size of new power generation capacity with and without capture was obtained. Six supplemental electricity generating technologies have been allowed for: subcritical pulverized coal‐fired (PC), PC with carbon capture (PC+CCS), integrated gasification combined cycle (IGCC), IGCC with carbon capture (IGCC+CCS), natural gas combined cycle (NGCC), and NGCC with carbon capture (NGCC+CCS). The optimization results showed that fuel balancing alone can contribute to the reduction of CO₂ emissions by only 3% and a slight, 1.6%, reduction in the cost of electricity compared to a calculated base case. It was found that a 20% CO₂ reduction at current electricity demand could be achieved by implementing fuel balancing and switching 8 out of 23 coal‐fired boilers to natural gas. However, as demand increases, more coal‐fired boilers needed to be switched to natural gas as well as the building of new NGCC and NGCC+CCS for replacing the aging coal‐fired power plants. To achieve a 40% CO₂ reduction at 1.0% demand growth rate, four new plants (2 NGCC, 2 NGCC+CCS) as well as carbon capture processes needed to be built. If greater than 60% CO₂ reductions are required, NGCC, NGCC+CCS, and IGCC+CCS power plants needed to be put online in addition to carbon capture processes on coal‐fired power plants. The volatility of natural gas prices was found to have a significant impact on the optimal CO₂ mitigation strategy and on the cost of electricity generation. Increasing the natural gas prices resulted in early aggressive CO₂ mitigation strategies especially at higher growth rate demands. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

碳中和背景下现代煤化工技术路径探索

从源头减碳、过程控碳、末端碳捕集封存和碳资源高附加值利用四个方面,分析了现代煤化工产业低碳发展的技术路径、对降低碳排放的效果以及未来应用前景。文中指出：源头减碳技术路径包括原料结构调整和能源结构调整,引入富氢和绿氢资源与煤炭进行碳氢互补,提高煤炭利用效率,并通过气代煤、电代煤,尤其利用弃风、弃电,可显著降低碳排放和工艺生产成本;过程控碳技术路径包括节能提效和开发革新技术,依靠现代煤化工技术进步,突破传统工艺瓶颈,是当前企业易于实施、应用较多的节能减排方式;末端碳捕集封存技术路径包括地质深层掩埋、驱油、强化深部咸水开采等,将工艺过程产生的高浓度CO₂通过低成本捕集,有效提高油气采收率,并为水资源匮乏地区提供额外供水;碳资源高附加值利用技术路径主要包括CO₂化学转化制高附加值及大宗化学品,国内正加快CO₂制低碳烯烃、芳烃、甲醇、碳酸酯的技术研发与示范应用,努力将CO₂从化石能源利用的终结排放者转化为碳循环利用的参与者,发展碳循环经济,减少碳排放。最后提出：未来将现代煤化工融入能源系统的大格局统筹考虑,推...     

A pilot-scale fireside deposit study of co-firing Cynara with two coals in a fluidised bed

Costs of biofuel production from energy crops can be reduced by applying the crop residues in heat and power production. Perennial herbaceous crops like Cynara cardunculus L. are challenging fuels because they tend to have high ash and chlorine contents. Coals, however, are often rich in aluminium silicates and sulphur, and co-firing of these biofuels with coal could be expected to reduce operational problems. In addition, CO₂ emissions are lower than during coal firing alone. Blends of Cynara and two coals, South African bituminous and Spanish sub-bituminous coal, were combusted in a 20 kW bubbling bed pilot reactor to ascertain the ability of the coals to reduce operational problems by alkali capture. The Cynara fuel sample contained almost 2 wt% chlorine. The South African coal was rich in kaolinite capable of capturing alkalies from chlorides to produce alkali aluminium silicate and HCl. The Spanish coal was rich in sulphur (mostly present as FeS₂), and produced high concentrations of SO₂ that partially oxidised to SO₃. The SO₃ can capture alkalies from chlorides by sulphation. Up to 30% Cynara, on energy basis, could be co-fired with Spanish coal without operational problems, whereas the same percentage of Cynara with South African coal led to strong Cl deposition. Co-firing of Cynara with both coals resulted in high HCl emissions (up to 1500 mg/Nm³ in 6% O₂). In addition, co-firing of the Spanish coal led to very high SO₂ emissions (up to about 16,000 mg/N m³ in 6% O₂). Thus, a power plant capable of firing such blends must be equipped with flue gas cleaning equipment for effective SO₂ and HCl capture in the flue gas channel after the superheaters, or else the quality of the Cynara must be markedly improved by changing the harvesting technology and fertilisers, which could be major sources of high ash and chlorine content in the fuel.     

Reduction of amine mist emissions from a pilot-scale CO2 capture process using charged colloidal gas aphrons

In the CO₂ capture process from coal-derived flue gas where amine solvents are used, the flue gas can entrain small liquid droplets into the gas stream leading to emission of the amine solvent. The entrained drops, or mist, will lead to high solvent losses and cause decreased CO₂ capture performance. In order to reduce the emissions of the fine amine droplets from CO₂ absorber, a novel method using charged colloidal gas aphron (CGA) generated by an anionic surfactant was developed. The CGA absorption process for MEA emission reduction was optimized by investigating the surfactant concentration, stirring speed of the CGA generator, and capture temperature. The results show a significant reduction of MEA emissions of over 50% in the flue gas stream exiting the absorber column of a pilot scale CO₂ capture unit.     

Recent progress of amine modified sorbents for capturing CO2 from flue gas

Under the Paris agreement, China has committed to reducing CO₂ emissions by 60%–65% per unit of GDP by 2030. Since CO₂ emissions from coal-fired power plants currently account for over 30% of the total carbon emissions in China, it will be necessary to mitigate at least some of these emissions to achieve this goal. Studies by the International Energy Agency (IEA) indicate CCS technology has the potential to contribute 14% of global emission reductions, followed by 40% of higher energy efficiency and 35% of renewable energy, which is considered as the most promising technology to significantly reduce carbon emissions for current coal-fired power plants. Moreover, the announcement of a Chinese national carbon trading market in late 2017 signals an opportunity for the commercial deployment of CO₂ capture technologies.Currently, the only commercially demonstrated technology for post-combustion CO₂ capture technology from power plants is solvent-based absorption. While commercially viable, the costs of deploying this technology are high. This has motivated efforts to develop more affordable alternatives, including advanced solvents, membranes, and sorbent capture systems. Of these approaches, advanced solvents have received the most attention in terms of research and demonstration. In contrast, sorbent capture technology has less attention, despite its potential for much lower energy consumption due to the absence of water in the sorbent. This paper reviews recent progress in the development of sorbent materials modified by amine functionalities with an emphasis on material characterization methods and the effects of operating conditions on performance. The main problems and challenges that need to be overcome to improve the competitiveness of sorbent-based capture technologies are discussed.     

Analyzing the energy intensity and greenhouse gas emission of Canadian oil sands crude upgrading through process modeling and simulation

This paper presents an evaluation of the energy intensity and related greenhouse gas/CO₂ emissions of integrated oil sands crude upgrading processes. Two major oil sands crude upgrading schemes currently used in Canadian oil sands operations were investigated: cokingbased and hydroconversion-based. The analysis, which was based on a robust process model of the entire process, was constructed in Aspen HYSYS and calibrated with representative data. Simulations were conducted for the two upgrading schemes in order to generate a detailed inventory of the required energy and utility inputs: process fuel, steam, hydrogen and power. It was concluded that while hydroconversion-based scheme yields considerably higher amount of synthetic crude oil (SCO) than the cokerbased scheme (94 wt-% vs. 76 wt-%), it consumes more energy and is therefore more CO₂-intensive (413.2 kg CO₂/m³ SCO vs. 216.4 kg CO₂/m³ SCO). This substantial difference results from the large amount of hydrogen consumed in the ebullated-bed hydroconverter in the hydroconversion-based scheme, as hydrogen production through conventional methane steam reforming is highly energy-intensive and therefore the major source of CO₂ emission. Further simulations indicated that optimization of hydroconverter operating variables had only a minor effect on the overall CO₂ emission due to the complex trade-off effect between energy inputs.     

Combustion characteristics of coal in a mixture of oxygen and recycled flue gas

The combustion of coal in a mixture of pure O₂ and recycled flue gas is one variant of a novel combustion approach called oxy-fuel combustion. With the absence of N₂, this approach leads to a flue gas stream highly enriched in CO₂. For many applications, this flue gas stream can then be compressed and sequestered without further separation. As a result, oxy-fuel combustion is an attractive way to capture CO₂ produced from fossil fuel combustion. When coal is burned in this O₂ and CO₂ rich environment, its combustion characteristics can be very different from conventional air-fired combustion. In CETC-O, a vertical combustor research facility has been used in the past years to investigate the combustion characteristics of several different coals with this variant of oxy-fuel combustion. This included flame stability, emissions of NO_x, SO_x and trace elements, heat transfer, in-furnace flame profiles and flue gas compositions. This paper will report some of the major findings obtained from these research activities.     

液化天然气、管道天然气与煤制天然气的比较分析

采用LCA方法对煤制天然气方案及其替代方案（俄罗斯进口管道天然气以及澳大利亚进口液化天然气）进行了评价,揭示了煤制天然气全生命周期各环节的环境效应。3种方案中,煤制天然气的CO₂等环境排放最高。煤制天然气对原材料价格的承受能力低下,随着褐煤价格的上涨,煤制天然气项目的经济性将受到较大的挑战。     

Selective transport of CO2, CH4, and N2 in coals: insights from modeling of experimental gas adsorption data

Selective adsorption and transport of gases in coal are important for natural gas recovery and carbon sequestration in depleted coal seams for environmental remediation. Gases are stored in coal mainly in the adsorbed state. In this study, the interaction energies of adsorbates (CO₂, CH₄, and N₂) and micropores with various widths are investigated using a slit-shape pore model. The experimental adsorption rate data of the three gases conducted on the same coal sample are numerically simulated using a bidisperse model and apparent diffusivities of each adsorbate in the macropore and micropore are determined. The results indicate that the relative adsorbate molecule size and pore structure play an important role in selective gas adsorption and diffusion in micropores. Generally, the microporous coals diffusion is activated and the apparent micropore diffusivities of gases in coal decrease strongly with increase in gas kinetic diameters. Apparent micropore diffusivity of CO₂ is generally one or two order of magnitude higher than those of CH₄ and N₂ because their kinetic diameters have the relation: CO₂ (0.33 nm)<N₂ (0.36 nm)<CH₄ (0.38 nm). In contrast to theoretical values, apparent macropore diffusivity of CO₂ is also larger than those of CH₄ and N₂, suggesting that coal has an interconnected pore network but highly constricted by ultra micropores with width <∼0.6 nm. It is also found that the apparent diffusivity strongly decreases with an increase in gas pressure, which may be attributed to coal matrix swelling caused by gas adsorption. Therefore, rigorous modeling of gas recovery and production requires consideration of specific interaction of gas and coal matrix.     

Comparison of solvent performance for CO2 capture from coal-derived flue gas: A pilot scale study

The performance of a proprietary solvent (CAER-B2), an amine-carbonate blend, for the absorption of CO₂ from coal-derived flue gas is evaluated and compared with state-of-the-art 30 wt% monoethanolamine (MEA) under similar experimental conditions in a 0.1 MWth pilot plant. The evaluation was done by comparing the carbon capture efficiency, the overall mass transfer rates, and the energy of regeneration of the solvents. For similar carbon loadings of the solvents in the scrubber, comparable mass transfer rates were obtained. The rich loading obtained for the blend was 0.50 mol CO₂/mol amine compared to 0.44 mol CO₂/mol amine for MEA. The energy of regeneration for the blend was about 10% lower than that of 30 wt% MEA. At optimum conditions, the blend shows promise in reducing the energy penalty associated with using industry standard, MEA, as a solvent for CO₂ capture.     

Minimizing fuel and environmental costs for a variable-load power plant (co-)firing fuel oil and natural gas: Part 1. Modeling of gaseous emissions from boiler units

This work was aimed at modeling of major gaseous emissions (NO_x, SO₃, SO₂, CO₂) from boiler units of a power plant firing (or co-firing) fuel oil and natural gas for variable operating conditions (load and load-related variables: excess air, flue gas recirculation, etc.). The emission rate of the pollutants for the co-firing was estimated for a particular boiler using these characteristics for the burning of each fuel in the boiler on its own and taking into account energy fractions (contributions) of fuel oil and natural gas to the boiler heat input. The gaseous emissions (in terms of emission concentrations, emission rates and specific emissions) from a 200-MW boiler unit firing low-S fuel oil and from a 310-MW boiler unit firing (or co-firing) medium-S fuel oil and natural gas were estimated and compared for 50–100% unit loads based on actual fuel properties and load-related operating variables of these units. Upper limit for the energy fraction of medium-S fuel oil was determined for the 310-MW boiler unit co-firing the two fuels with the aim to meet the national emission standard for SO₂.     

High-performance oxygen transport membrane reactors integrated with IGCC for carbon capture

Precombustion carbon capture is an effective strategy to reduce large-scale CO₂ emissions, which is mainly used in the area of integrated gasification combined cycle (IGCC) power plants. Oxygen transport membranes (OTMs) were suggested as the air separation unit to produce high purity oxygen for the gasifier. However, the improvement in efficiency was limited. Here, a new IGCC process is reported based on a robust OTM reactor, where the OTM reactor is used behind the coal gasifier. This IGCC-OTM process fulfills syngas oxidation, H₂ production, and carbon capture in one unit, thus a significant decrease of the energy penalty is expectable. The membrane reactor does not use noble metal components, and exhibits high hydrogen production rates, high hydrogen separation factor (10³–10⁴), and stable performance in a gas mixture mimicking real syngas compositions from a coal gasifier with H₂S concentrations up to 1,000 ppm.     

Nonlinear optimization of steel production using traditional and novel blast furnace operation strategies

The high energy requirements in primary steelmaking make this industrial sector a major contributor to the global emissions of carbon dioxide. Ways to suppress the use of fossil reductants and the emissions from the processes should therefore be developed. The present work applies simulation and optimization for studying the economic feasibility of recycling blast furnace top gas to the combustion zones after CO₂ stripping. The study comprises the unit processes in an integrated steel plant, paying special attention to the blast furnace and the preheating of the blast or the recycled top gas. The system is optimized with nonlinear programming with respect to some central variables under different CO₂ sequestration and emission costs, which yields information about the economic feasibility of the concept. It is demonstrated that the optimal states of the plant show complex transitions, where the costs play a decisive role. It is also shown that hot gas recycling with CO₂ capture and storage would dramatically reduce the harmful emissions from the process. The conditions under which top gas recycling is economically feasible are also reported, as well as the effect of omitting oil injection in a blast furnace with top gas recycling.