Recovery of CO2 from Units of Steam Methane Reforming at Sines
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Recovery of CO 2 from units of Steam Methane Reforming at Sines Refinery Alexandre, André 1,2 , Alves, Sebastião 1, Campos, Cristina 2 1Department of Chemical Engineering, Instituto Superior Técnico, Lisbon, Portugal 2 Technical Refining Staff, Galp Energia, Lisbon, Portugal Abstract This master degree thesis results from an internship done at Technical Refining Staff of Galp Energia between March and September of 2011and had as main objective to select the CO 2 recovery process to be applied in hydrogen units located in Sines Refinery. Initially, was elaborated a general study on the market for liquid carbon dioxide in Europe and particularly in Iberia, being also analyzed the different processes of recovery it with matching industrial existence. Subsequently, were examined the existing two Hydrogen units, as they constitute the source of carbon dioxide. The comparison of the recovery processes of CO 2, within this academic analysis, made possible to select the process FlashCO 2, as the one with highest probability of being used in Sines. Then, based up on this process, were estimated the capacities of CO 2 units for extreme conditions, taking into account the utilization rates of hydrogen units concerned. Therefore, it was also completed an analysis of the possible technical and logistical implementation of a CO 2 unit at Sines Refinery. Finally, an economic analysis allowed to conclude that the CO 2 unit, downstream of the hydrogen production plant HR, is feasible, being the minimum rate of operation below the average of the units in the European Union. Keywords: CO 2 capture, H2 production, tail gas , flashCO 2 process, Sines Refinery 1. Introduction charcoal. Afterwards, Hoffmann discovered Carbon dioxide is normally present at that this gas is an acid gas and, Black gaseous state (atmospheric conditions) and showed is lethal effect on animal life. its presence has been known since the XVI Although, Lavoisier was the first to century [1]. Van Helmont was the first to demonstrate the existence of this gas, when recognize it when he prepared and isolated he proved its composition and named it the gas by various routes: fermentation, carbonic acid. action of acids on carbonates, burning of The commercial exploitation of carbon dioxide began with attempts to produce artificial mineral waters and its Nowadays, current uses for CO 2 are in development was carried on by Faraday and the beverage and alimentary industry Thilorier, who realized experiments on the (higher relevance in Europe), water liquefaction of gases. Thilorier succeeded treatment, enhanced oil recovery (EOR, in experiments on the expansion, vapor particularly in the U.S.A.), agriculture, fire pressure, density, and enthalpy changes of extensor and inert agent, metals fabrication the liquid CO 2 during evaporation, and he industry and chemical application in was the 1 st to produce solid carbon dioxide. production of urea and methanol. The majority of the carbon dioxide generated in the world is a by product of 2. Market Analysis ammonia and hydrogen production. As so, The liquid CO 2 merchant market was there aren’t processes for production of CO 2 analysed in Portugal, Iberia and Europe. and the corresponding raw materials, but In Portugal, the liquid CO 2 production there are recovery processes and the sources is only made by Air Liquide in Estarreja. where the gas can be recovered [1]. Recently, in 2009, this company made an Other sources are the flue gases of upgrade of its capacity to 29 kton/year. power plants (natural gas or coal based), There were two other units in Lavradio cement units and limekilns and in sugar connected to ammonia production, which fermentation units like bio-ethanol begun lay-off in 2007 and closed definitely factories. The last sources of CO2 can be in 2009. Currently, the Portuguese considered as the natural occurrence of the production is around 3,5 kton/year and the gas in caverns (due to precedent volcanic consumption about 25-35 kton/year. activity) or the presence in natural gas wells In Spain, the liquid CO 2 production is with very high concentrations. made by Praxair, Air Liquide, Linde, Air Products and Neoelectra (decreasing order Table 1 - Comparison of CO 2 purity and of capacity), with total production and recovery cost by source Purity Recovery consumption close to 420 kton/year, being Source (% mol) Cost the installed capacity near 693 kton/year. 15 - 20 % ++ Therefore, in Iberia the installed Hydrogen unit 40 - 50 % +++ capacity is 722 kton/year, from the Ammonia unit ≈ 97 % + following sources: hydrogen (57%), ammonia (22%), bio-ethanol (11%) and Flue Gas from 10-20 % ++++ power plants (10%). The equivalent total Power plant consumption is, approximately, 450 Bioethanol unit > 80 % ++ kton/year. Natural source > 90 % + Limekilns ≈ 40 % +++ 3. H2 production in Sines Refinery The hydrogen production in Sines Refinery is carried out by two units: HI of 2003, with a maximum capacity of 30 3 kNm H2/h, and HR from 2011, with 90 3 kNm H2/h [2]. Figure 1 - Geographic location of Refineries and CO 2 units in Iberia In Europe, the merchant of liquid carbon dioxide is around 3600 kton/year, to a corresponding capacity of 5600 kton/year. Here, there is also a production of 1700 Figure 3 - HI unit kton/year that is stored, in CCS activities. The sources of CO 2 in Europe have a Both of these units produce H 2 by different distribution than in Iberia, being Steam Methane Reforming process, with the the units of ammonia the main origin main difference in the presence of Pre- (52%), followed by the units of hydrogen Reforming in the case of HR unit [3]. (30%) and bio-ethanol (6%). The others The main advantage of the introduction sources include CO from caverns (Italia, 2 of Pre-Reforming in the most recent unit is Hungary), from ethylene oxide units supplied by the savings in the combustion (Germany, Belgium) and power plants of fuel to fired heater of the SMR , as also (Spain, Germany). The European market its the lower production of vapour for export controlled mainly by three companies as and the higher feedstock flexibility [4]. shown in Figure 2. 4. CO 2 capture processes 18,3% The capture of CO 2 can be divided in 41,3% 22,5% three main categories: pre-combustion, 17,7% post-combustion and oxyfuelling [5]. In this case, the capture of CO 2 from a hydrogen Air Liquide Linde Yara Outros unit is of the first category and is realized in the syngas stream (inlet of PSA) or in the Figure 2 - Market shares by total capacity tail gas stream (outlet purge gas form PSA). The major processes available can be 4.2. Physical absorption grouped as follows: The physical absorption can be utilized • Absorption Processes when the CO 2 concentration is between 15 • Adsorption Processes and 40% of the stream (molar fraction) and • Membrane Separation the partial pressure of the gas in the stream • Cryogenic separation is high. The process bases are quite similar to To remove the CO 2 from the streams the chemical absorption with the significant mentioned above, all of the process options divergence of using a physical agent are viable. However, the capture of CO 2 in instead, and that the physical absorption is Syngas should be done with absorption favoured at low temperatures. As so, the processes, preferably chemical type (amine main processes to remove CO 2 are: Selexol MDEA), and in tail gas must be utilized a (DMPEG), Purisol (NMP), Fluor Solvent Cryogenic separation. (propylene carbonate) and Rectisol process (methanol). The last two processes are the 4.1. Chemical absorption and MDEA most important and used because their There are a variety of amines that can solvents prove to have higher absorption be utilized in the treatment of acid gases. capacities relative to CO 2. Furthermore, the To remove of CO at low concentrations, 2 Rectisol has the lowest solvent circulation i.e. until 15% of the stream (molar rate and requires less energy [6]. fraction), the most widely used amines is the MEA, DEA and MDEA [5]. 4.3. Membrane separation The comparison between this amines Membrane systems have been reveals that MDEA is the most indicated particular utilized in the treatment of amine to remove CO 2, because it doesn’t natural gas with high concentration of acid react with this gas (so it doesn’t stimulate gases like CO 2. As main advantages, it has the corrosion problems), has higher uptake higher capacity to adapt to variations of of absorption of CO 2 and requires less CO 2 in the feed and the spatial requirements energy in regeneration step. As drawback of the installation are low [8]. it’s quite more expensive then the others and it can’t react directly with CO 2, so it is 4.4. Cryogenic separation necessary a primary dissolution of the gas Cryogenic separation has special in water (slow reaction). However, this last utilization in streams where the CO 2 disadvantage can be overwhelmed with the concentration is above 40% (%mol), being addiction of an activator – aMDEA[6],[7]. ideally to remove CO 2 from tail gas stream. The MDEA process can even achieve This separation path includes the CO removal rates higher than 95% [7]. 2 following operations to obtain CO 2: compression, cooling, expansion and increases the CO 2 removal rate and distillation (to higher purity requirements). produces a stream of off-gas (mainly The main disadvantages of these processes composed by H 2, CO, CH 4 and residual are related to the conditions of operation: CO 2) that can be send to a PSA or high pressure and low (negative) membrane unit for H 2 recovery.