Methanation in Synthetic Natural Gas (SNG) Production

Methanation in Synthetic Natural Gas (SNG) ProductionMethanation is the dish come out of the closet of producing methane from H2 and CO. Methane (an odourless and colourless feature, composed of four total heat molecules attached to genius one C molecule) is fix in ingrained float that we jackpot practice session in our homes for energy. Methane institute in raw(a) float is sufferd by anaerobic bacteria, which break down organic material and the waste increase is the natural fellate. The natural gas that is sought after by companies such as BP drilling for oil and gas was produced by anaerobic bacteria millions of eld ago. Methane is employ in m either growthes some of which ar explained be crushed. We will principally con postr methanation in the output of Substitute Natural Gas (SNG) as this can be procedured instead of natural gas which has check resources and supply.Methanation is the reverse reception of go methane re machinateing. It is one of the mo st important step in ammonium hydroxide plants as the COx produced in the general steam reforming forge pack to be sepa sayd from the H2, as the H2 is to be uptaked for ammonia discount. This assist is excessively referred to as purification methanation. The content of oxides of carbon in the increaseion of ammonia must be reduced to a very low direct to prevent gas pedal poisoning2. After the low temperature shift (LTS) chemic chemical chemical reaction and deduction of CO2, the methanation reaction is utilise to remove any symmetry COx from the butt stream before ammonia synthesis. distinction amounts of CO and CO2 be reacted with hydrogen in the presence of a plate note oxide accelerator to produce a mixture of methane and water. This process removes the remainder 0.2-0.5% CO and 0.1%-0.2% CO2 to about 5ppm (it is vital to in the issue of ammonia to remove the COx as even a low level significantly reduces the methanation rate) by reduction to methane with h ydrogen in a fixed- whop nuclear reactor, with a 15-35 wt% Ni/Al2O3 gun (2).This accelerator is usually prepargond by impregnating laid-back come out of the closet argona - Al2O3 with a soluble Ni salt. MgO can be utilise to impede sintering of the active Ni crystallites. For this process methanation is normally carried out in an adiabatic, fixed-bed reactor at 30 atm, with an inlet temperature of 300C and an exit temperature of 365C. This reaction is richlyly exothermic and the temperatures of the bed atomic number 18 kept below 400C so that accelerator pedal sintering and carbon deposit is prevented. 3What is SNG?Substitute/Synthetic Natural Gas (SNG) is similar to natural gas but produced from ember or biomass (e.g. wood, straw, waste). It is a manufactured product which is chemically similar to natural gas. Natural gas is the worldwide enkindle of choice but there is limited supply, so SNG is one of the options to curb this. Producing SNG from biomass is overly cons idered to be thought of as green gas as it avoids extra CO2 emissions, because it is carbon neutral. SNG has many advantages some of which atomic number 18the already existing gas supply infrastructure (e.g. pipelines) which allow the gas to be distributed without a country such as the USA and besides worldwidehigh conversion debatencyEfficient final use technologies that argon well-established e.g. Compressed Natural Gas (CNG cars), Combined Heat and designer (CHP), and Heating.What is the methanation process and how is it used in the production of SNG?CO + 3H2 CH4 + pee The reaction between H2 and CO can produce a number of unlike products depending on the reaction conditions, the catalyst used and the stoichiometry of the reactants. The reaction of great lodge in to us is the one producing methane. This reaction over a nickel catalyst was first reported by Sabatier and Senderens (1902, 1905) and even though a cover of research has gone into which catalyst is the best fo r methanation, nickel has continued as the key catalyst for methanation because of its selectivity for the production of methane, high activity, and inexpensiveness comp atomic number 18d to other catalysts. Catalysts involved in methanation operate for a long time in catalyst beds and for that intellect catalyst life and strength are also of major importance. some problems such as sulphur poisoning are involved with these catalysts they are mentioned in a later section of this report.5The to a higher place off reaction is exothermic, releasing heat (the delta H values are negative presentation this) and the forward reaction is favoured by low temperature and high pressure, Product gas with a high fraction of CH4 can whole be generated at low temperature (300-350C) and high pressure 20 bar.6 We also chicane from Le Chateliers Principle that pressure favours the side with fewer moles which in this case is the forward reaction producing methane and water, so a high pressure should be used.The production of methane is a fundamental step in the process of manufacturing that gas from burn to produce SNG. The typical methanation process involved in SNG consists of three fixed-bed methanating acquaints that are used in series with a fixed-bed of catalyst. A single level process can and has also been used for methanation, such as the IRMA Methanation sail plant KFA project, the conditions for this single typify were P = 30 bar T = 250-700C (1 stage) Volumetric flow rate = 600m3 (STP)h -1, (synthesis gas) 1100 operating hours since 19817. The three stage methanation process consists ofTotal Gasification of the coal in steam, possibly with group O, C+H2OH2+ COChanging the ratio of H2 to CO in the product gas by the water gas shift reaction, and then removing any residual CO2. CO+H2OH2+CO2The hydrogen and carbon monoxide are converted to methane (following the removal of damaging material to the process such as hydrogen sulphide) ontogeny a catalyst (n ickel is the most common for this process as explained later in this report.). This final stage is a straight by dint of reactor operating at lower temperature than that of the previous stages as shown in Fig.1 below. This gives methane which contains typically less than 3% H2, 0.1% CO and has a thermal efficiency of approximately 70% for the total process. This methane produced can then be use in the production of SNG. CO + 3H2 CH4 + H2O 8As the temperature need to be controlled the product gases are recycled over the first stages with interstage cooling which prevents the temperature from change magnitude and also means that the process is more(prenominal) efficient as the gases are recycled and you dont expect to put extra cooling in to keep the temperature from hike which saves funds. The avoiding of high temperatures also protects the catalysts, if the reaction temperature becomes too high not only is the equilibrium state of the hydrogenation reaction adversely affecte d but the catalyst life is shortened by sintering of the metal particles9.Fig. 1 shows the three-stage process with fixed-bed reactors and the same thermodynamic equilibrium temperatures for the synthesis gas with 10% CH4 at stage one and the desired dry product gas with more than 80% CH4. This diagram also shows that after the first stages the temperature decreases again and this is to avoid high temperatures in order to protect the catalyst but also to domain thermodynamic equilibrium at low temperatures. This is done by product gas recycling cooling as explained before.It is also important to know that when producing SNG by methanation the CO and H2 (i.e. the reactants) will contain a lot more of the monoxide than in the methanation process used for ammonia synthesis. In ammonia synthesis only a small amount of monoxides (less than 1%) are found however in SNG production the methanation process reactants can have 30-50% of the monoxide. It is also important to know that in the purification methanation even a low amount of monoxides can seriously deteriorate the methanation process by catalyst poisoning.8This picture shows the process of coal gasification, and then the products creation cleaned and readied for methanation. Gasification is simply the process of producing coal gas, a mixture of CO and H2 which is known as syngas. This syngas can then be used in the methanation process producing SNG.How methanation is used in patienceFrom the 1970s quite a few methanation processes have been veritable which consist of fixed bed and fluidised bed methanation. Most of the methanation processes used in industry use fixed bed reactors (used for the methanation in ammonia production, expound before) as they are the most common type of reactor used in industry for many reasons such as having the simplest multi-phase reactor word form where the solid phase is stationary and complications arising from the second phases mixing mode are not present.10 However, som e processes use fluidised bed reactors also as fluidized bed methanation presents the advantage of good heat transfer from the process gas side to the cooling medium and the advantage of particular simplicity when exchanging the catalyst in case of catalyst poisoning or catalyst deactivation.11 The choice of the reactor also depends on the size of the reactor needed and the follows of apparatus and operating (does it need to be cleaned regularly or not as this costs money ad stops production). atomic number 53 of the biggest plants to make SNG from coal-derived syngas was started up in 1984 the Great Plains Synfuels Plant of Dakota Gasification Co. which cost $2.1billion was the only SNG plant of that plateful operating in the world. The plant uses Lurgi GmbH gasifiers (a steel construction where around all(prenominal) time 8 tons of coal is fed into a compartment at its top, known as a coal lock, which is then sealed with a gas macrocosm fed into it ahead of the bottom of the lock curtain raising to feed coal, in this plant the coal is Lignite which is 60-70%carbon, into the body of the gasifier, this builds up high pressure and the high pressure and temperature feed of steam and oxygen in the gasifier decompose the lignite to produce syngas). The syngas is then converted to SNG using DPT methanation catalysts. This plant produces approximately 153 million ft3/day of SNG which is piped throughout the US. This facility has also implemented CCS (carbon capture and storage) and as of the end of last year (31/12/2009) it has captured more than 17.4 million m.t. of CO2.12As you can imagine $2.1billion is a lot of money and was expenditure even more in 1984 showing that using methanation to produce SNG is not a small venture but a major player in the search for more fuel as the worlds gas and oil reserves are depleting. In 2009 the plant produced $264.7 million worth of SNG out of total revenue of $426.1 million. The operating costs for this plant (including maintenance) were $38,504,111.13This shows that the coronation of $2.1billion was a really good decision not only in price of producing SNG from methane but also a really great logical argument return.FIGURE 3 DPTs methanation process is a refinement and further development of the Catalytic Rich Gas (CRG) process, which was first developed by British Gas Corp. in the late 1960s to convert naphtha into town gas. The process involves several methanator reactors in series, with heat recovered from the exothermic reaction (CO + 3H2 CH4 + H2O) used to raise high pressure superheated steam and to preheat the feed. Each reaction stage consists of a fixed bed of CRG catalyst operating adiabatically.12However, forward-looking and more efficient processes are being implemented in industry, that in particular focus on the conversion of biomass, such as the Milena process in the Netherlands. The ECN (Energy Research Center of the Netherlands) has developed a biomass gasification technolo gy with high gas efficiency and a high methane yield which allows it to be used for gas-engine applications. This process has been given the severalise Milena, and the product gas can be upgraded to SNG and ECN has the rivalry to turn this into large scale SNG production with an energy efficiency of 70%. This would be much needed as the Netherlands relies on 50% of its energy from natural gas (which is not renewable) so using SNG for biomass would be a substitute for this and the biomass is available in large quantities and it a lot dry cleaner and friendlier to the environs than natural gas.14The biomass has to be converted into SNG by gasification and then methanation (theses processes and their outlines have been mentioned before). This allows it to reach efficiency, say from wood, up to 65% (this efficiency is calculated from the chemical energy output of SNG compared to the chemical energy input of wood). Biomass (e.g. wood and straw) being used to produce SNG has the advan tage over coal lowlyd SNG of being almost CO2 neutral, without CCS. Production of synthetic natural gas (SNG) from coal and dry biomass.4Catalyst UsedThe main catalysts that are used as methanation catalysts are nickel or nickel supported catalysts. This is because the key catalyst properties of nickel are excellent for methanation as it has long life, high activity, selectivity for the organization of methane in preference to other hydrocarbons and the low cost compared to other catalysts. One of the main disadvantages for nickel catalysts is the sensitivity to poisoning by sulphur, other catalysts are available that are sulphur-resistant and also catalyse the methanation reaction but these are much less active than nickel resulting in a unhurried rate of reaction.For example, one manufacturers catalysts are formulated on Ca aluminate base with the active nickel incorporated in a NiO/MgO solution, this leads to negligible nickel sintering.10In catalytic methanation many promoters for nickel have been studied such as copper, zinc oxide, magnesia, iron, calcium oxide, chromia and alumina. What was found was that alumina, chromia and magnesia were the best promoters in terms of activity and thermal stableness. It was also found that for thermal and mechanical stability the best of a number of NiO methanation catalysts on supports of A12O3, a mixture of A12O3 and CaO, MgO, SiO2 and Cr2 O3 was NiO-AI2O3 containing 35% NiO.15 Many other factors are taken into consideration when choosing the catalyst for the methanation process. These are explained below(i) Sulphur poisoning.Sulphur poisoning causes the methanation catalysts, to become inactive, this is because the reactants have brought in an alien molecule and this sits on the active site, the reactants now have to compete with this poison for the active sites and this results in a spill of the active locate area therefore decreasing the rate of reaction.10(ii) Thermal stability.This reaction is super exothe rmic it is very important to make sure that the reaction temperature does not become too high because it affects the equilibrium state of the reaction unfavorably and the catalyst life decreases cod to sintering of the metal particles, where the particles come together, decreasing the surface area compared to when no sintering took place, thus less reaction is obtained. As mentioned previously the reaction temperature for this reaction is 300C-400Cfor which the nickel based catalysts used are sufficient in terms of longevity and activity. But there are catalysts tat are able to operate at high temperatures than nickel based catalysts and these would be even more desirable as the higher the temperature at which the heat of methanation is released the more effectively can it contribute to overall thermal efficiency of the conversion process, for example of coal to SNG, it is also worthwhile to notice that at these higher temperatures the problem of sulphur poisoning decreases due to instability of the catalyst metal sulphide9. So why is it that in industry the use of catalysts that are suitable for operation at higher temperatures are not selected and for e.g. nickel catalysts are favoured? This is due to the fact that it is not unceasingly feasible to use the best catalyst for the process as it may cost too much to buy.(iii) Coke formation and foulingCarbon in its unreactive form, or as Ni3C produced on the Nickel catalyst, causes a loss of catalyst activity9. The coke formed blocks the reactants from reaching the active sites and the fouling is caused by the reaction forming a by-product which then sits on the active site, masking it. It is doable to avoid the unwanted carbon formation in the manufacture of SNG by controlling the water gas shift reaction. This is the 2nd step shown in figure 2 previously.The cost of nickel catalysts varies as the price of nickel fluctuates. The suppliers of these catalysts do not sell just a few kilograms of the catalys t they have a minimum orders quantity, e.g. 20 tons at the rate of $15000-$30000 per ton. An example of a Methanation catalyst used in industry is the SG-9701 (the name may be fancy but it is mostly nickel as shown in the table) produced by the global leader in catalysis, BASF who have found that although the catalysts operate at low temperature and show good conversion range in the Methanation process, they eventually begin to age and lose their effectiveness, that is why through their current research they have identified that Methanation Catalyst relies on the right combination of nickel oxide technology on an alumina matrix. However, through minute control of composition and geometry and the addition of a Rare Earth promoter, a number of performance improvements are achieved, these improvements are temperature resistance and long mechanical life. BASFs methanation catalyst also boasts a superior physical makeup reducing deterioration that can lead to increased pressure drop in the system16For the future?Another SNG project was decided upon in this April between ConocoPhillips and POSCO (a Korean steel-manufacturing company) in which ConocoPhillips E-Gas technology is being used with POSCOs Gwangyang coal to SNG project. This facility has targeted production of 500,000 m.t. of SNG I will not go further with this project as the methanation technology to be used has not yet been announced and a new technology to produce SNG using petroleum coke (petcoke) (an move on technology that captures and sequesters CO2 emissions from an industrial source) is to be implemented with this at a further stage. 12Hydromethanation-Peabody Energy and GreatPoint Energy Mass recently sign-language(a) an agreement to produce SNG from coal, H2 from coal and also CCS projects. These are wanted to be developed with Bluegas technology, which uses catalytic Hydromethanation to produce H2 and SNG. The process is more efficient and cost effective than conventional gasification rou tes to SNG. In the bluegas process a propriety catalyst is dispersed with the feedstock (coal, petcoke, or biomass), and the mixture loaded into the reactor. Pressurized steam is injected from below to fluidize the mixture, which reacts to form CH4, CO2, H2 and CO.12There is also a German-Austrian project that wants to produce methane from extra galvanizing energy that has been generated from solar or wind power and a process that combines methanation with electrolysis has been developed at the Center for Solar Energy and Hydrogen Research, Germany. final stageMethanation is a very important process especially in todays environment where we look to reduce CO2 emissions further and producing SNG from biomass using the methanation process does this or else than using natural gas. Methane is used in the gas that provides our homes with energy and heating. We need to find even more efficient processes like the ones described above that use methanation to produce SNG.