Methanation is the procedure of bring forthing methane from H2 and CO. Methane ( an odourless and colourless gas, composed of four H molecules attached to one C molecule ) is found in natural gas that we can utilize in our places for energy. Methane found in natural gas is produced by anaerobiotic bacteriums, which break down organic stuff and the waste merchandise is the natural gas. The natural gas that is sought after by companies such as BP boring for oil and gas was produced by anaerobiotic bacteriums 1000000s of old ages ago. Methane is used in many procedures some of which are explained below. We will chiefly see methanation in the production of Substitute Natural Gas ( SNG ) as this can be used alternatively of natural gas which has limited resources and supply.
Methanation is the rearward reaction of steam methane reforming. It is one of the most of import stairss in ammonium hydroxide workss as the COx produced in the overall steam reforming procedure demand to be separated from the H2, as the H2 is to be used for ammonia synthesis. This procedure is besides referred to as ‘purification ‘ methanation. The content of oxides of C in the production of ammonium hydroxide must be reduced to a really low degree to forestall accelerator poisoning2. After the low temperature displacement ( LTS ) reaction and tax write-off of CO2, the methanation reaction is used to take any residuary Cyclooxygenase from the procedure watercourse before ammonia synthesis. Trace sums of CO and CO2 are reacted with H in the presence of a nickel oxide accelerator to bring forth a mixture of methane and H2O. This procedure removes the residuary 0.2-0.5 % CO and 0.1 % -0.2 % CO2 to about 5ppm ( it is critical to in the production of ammonium hydroxide to take the COx as even a low degree significantly reduces the methanation rate ) by decrease to methane with H in a fixed-bed reactor, with a 15-35 wt % Ni/Al2O3 accelerator ( 2 ) .This accelerator is normally prepared by infusing high surface country I?- Al2O3 with a soluble Ni salt. MgO can be used to hinder sintering of the active Ni crystallites. For this procedure methanation is usually carried out in an adiabatic, fixed-bed reactor at 30 standard pressures, with an inlet temperature of 300A°C and an issue temperature of 365A°C. This reaction is extremely exothermal and the temperatures of the bed are kept below 400A°C so that accelerator sintering and C deposition is prevented. 3
What is SNG?
Substitute/Synthetic Natural Gas ( SNG ) is similar to natural gas but produced from coal or biomass ( e.g. wood, straw, waste ) . It is a manufactured merchandise which is chemically similar to natural gas. Natural gas is the world-wide fuel of pick but there is limited supply, so SNG is one of the options to get the better of this. Producing SNG from biomass is besides considered to be thought of as ‘green gas ‘ as it avoids excess CO2 emanations, because it is carbon impersonal. SNG has many advantages some of which are:
the already bing gas supply substructure ( e.g. grapevines ) which allow the gas to be distributed throughout a state such as the USA and besides worldwide
high transition efficiency
Efficient concluding usage engineerings that are well-established e.g. Compressed Natural Gas ( CNG autos ) , Combined Heat and Power ( CHP ) , and Heating.4
What is the methanation procedure and how is it used in the production of SNG?
CO + 3H2 a†” CH4 + H2O The reaction between H2 and CO can bring forth a figure of different merchandises depending on the reaction conditions, the accelerator used and the stoichiometry of the reactants. The reaction of great involvement to us is the one bring forthing methane. This reaction over a nickel accelerator was foremost reported by Sabatier and Senderens ( 1902, 1905 ) and even though a batch of research has gone into which accelerator is the best for methanation, Ni has continued as the cardinal accelerator for methanation because of its selectivity for the production of methane, high activity, and inexpensiveness compared to other accelerators. Catalysts involved in methanation operate for a long clip in accelerator beds and for that ground accelerator life and strength are besides of major importance. Many jobs such as sulfur toxic condition are involved with these accelerators ; they are mentioned in a ulterior subdivision of this report.5
The above forward reaction is exothermal, let go ofing heat ( the delta H values are negative demoing this ) and the forward reaction is favoured by low temperature and high force per unit area, “ Product gas with a high fraction of CH4 can merely be generated at low temperature ( 300-350A°C ) and high force per unit area & gt ; 20 saloon. “ 6 We besides know from Le Chatelier ‘s Principle that force per unit area favours the side with fewer moles which in this instance is the forward reaction bring forthing methane and H2O, so a high force per unit area should be used.
The production of methane is a cardinal measure in the procedure of fabrication that gas from coal to bring forth SNG. The typical methanation procedure involved in SNG consists of three fixed-bed methanating phases that are used in series with a fixed-bed of accelerator. A individual phase procedure can and has besides been used for methanation, such as the IRMA Methanation pilot works KFA undertaking, the conditions for this individual phase were P = 30 saloon ; T = 250-700A°C ( 1 phase ) ; Volumetric flow rate = 600m3 ( STP ) H -1, ( synthesis gas ) ; 1100 operating hours since 19817. The three phase methanation procedure consists of:
Entire Gasification of the coal in steam, perchance with O, C+H2Oa†”H2+ CO
Changing the ratio of H2 to CO in the merchandise gas by the H2O gas displacement reaction, and so taking any residuary CO2. CO+H2Oa†”H2+CO2
The H and C monoxide are converted to methane ( following the remotion of damaging stuff to the procedure such as H sulfide ) utilizing a accelerator ( Ni is the most common for this procedure as explained subsequently in this report. ) . This concluding phase is a consecutive through reactor operating at lower temperature than that of the old phases as shown in Fig.1 below. This gives methane which contains typically less than 3 % H2, 0.1 % CO and has a thermic efficiency of about 70 % for the entire procedure. This methane produced can so be usage in the production of SNG. CO + 3H2 a†” CH4 + H2O 8
As the temperature needs to be controlled the merchandise gases are recycled over the first phases with interstage chilling which prevents the temperature from increasing and besides means that the procedure is more efficient as the gases are recycled and you do n’t hold to set excess chilling in to maintain the temperature from lifting which saves money. The avoiding of high temperatures besides protects the accelerators, “ if the reaction temperature becomes excessively high non merely is the equilibrium province of the hydrogenation reaction adversely affected but the accelerator life is shortened by sintering of the metal atoms ” 9.
Figure 1 ( B. HOHLEIN, H. NIESSEN, J. RANGE. ( 1984 ) . Nuclear Engineering and Design. Methane from synthesis gas and operation of high-temperature methanation pg 2 )
Fig. 1 shows the three-stage procedure with fixed-bed reactors and the corresponding thermodynamic equilibrium temperatures for the synthesis gas with 10 % CH4 at phase one and the coveted dry merchandise gas with more than 80 % CH4. This diagram besides shows that after the first stages the temperature decreases once more and this is to avoid high temperatures in order to protect the accelerator but besides to make thermodynamic equilibrium at low temperatures. This is done by merchandise gas recycling chilling every bit explained before.
It is besides of import to cognize that when bring forthing SNG by methanation the CO and H2 ( i.e. the reactants ) will incorporate a batch more of the monoxide than in the methanation procedure used for ammonia synthesis. In ammonia synthesis merely a little sum of monoxides ( less than 1 % ) are found nevertheless in SNG production the methanation procedure reactants can hold 30-50 % of the monoxide. It is besides of import to cognize that in the ‘purification ‘ methanation even a low sum of monoxides can earnestly deteriorate the methanation procedure by accelerator poisoning.8
Fig. 2 – Coal ( B. HOHLEIN, H. NIESSEN, J. RANGE. ( 1984 ) . Nuclear Engineering and Design. Methane from synthesis gas and operation of high-temperature methanation pg 2 )
This image shows the procedure of coal gasification, and so the merchandises being cleaned and readied for methanation. Gasification is merely the procedure of bring forthing coal gas, a mixture of CO and H2 which is known as syngas. This syngas can so be used in the methanation procedure bring forthing SNG.
How methanation is used in industry
From the 1970s rather a few methanation procedures have been developed which consist of fixed bed and fluidised bed methanation. Most of the methanation processes used in industry usage fixed bed reactors ( used for the methanation in ammonia production, described earlier ) as they are the most common type of reactor used in industry for many grounds such as holding the simplest multi-phase reactor constellation where the solid stage is stationary and complications originating from the 2nd stages blending manner are non present.10 However, some procedures use fluidised bed reactors besides as “ fluidized bed methanation presents the advantage of good heat transportation from the procedure gas side to the chilling medium and the advantage of peculiar simpleness when interchanging the accelerator in instance of accelerator toxic condition or accelerator inactivation. “ 11 The pick of the reactor besides depends on the size of the reactor needed and the costs of apparatus and operating ( does it necessitate to be cleaned on a regular basis or non as this costs money ad stops production ) .
One of the biggest workss to do 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 lone SNG works of that graduated table operating in the universe. The works uses Lurgi GmbH gasifiers ( a steel building where around each clip 8 dozenss of coal is fed into a compartment at its top, known as a coal lock, which is so sealed with a gas being fed into it in front of the underside of the lock gap to feed coal, in this works the coal is Lignite which is 60-70 % C, into the organic structure of the gasifier, this builds up high force per unit area and the high force per unit area and temperature provender of steam and O in the gasifier decompose the brown coal to bring forth syngas ) . The syngas is so converted to SNG utilizing DPT methanation accelerators. This works produces about 153 million ft3/day of SNG which is piped throughout the US. This installation has besides implemented CCS ( C gaining control and storage ) and as of the terminal of last twelvemonth ( 31/12/2009 ) it has captured more than 17.4 million m.t. of CO2.12As you can conceive of $ 2.1billion is a batch of money and was deserving even more in 1984 screening that utilizing methanation to bring forth SNG is non a little venture but a major participant in the hunt for more fuel as the universe ‘s gas and oil militias are consuming. In 2009 the works produced $ 264.7 million worth of SNG out of entire gross of $ 426.1 million. The operating costs for this works ( including care ) were $ 38,504,111.13This shows that the investing of $ 2.1billion was a truly good determination non merely in footings of bring forthing SNG from methane but besides a truly great concern return.
FIGURE 3 “ DPTs methanation procedure is a polish and farther development of the Catalytic Rich Gas ( CRG ) procedure, which was foremost developed by British Gas Corp. in the late sixtiess to change over naphtha into town gas. The procedure involves several methanator reactors in series, with heat recovered from the exothermal reaction ( CO + 3H2 a†” CH4 + H2O ) used to raise high force per unit area superheated steam and to preheat the provender. Each reaction phase consists of a fixed bed of CRG accelerator runing adiabatically. “ 12
However, new and more efficient procedures are being implemented in industry, that particularly focus on the transition of biomass, such as the Milena procedure in the Netherlands. The ECN ( Energy Research Center of the Netherlands ) has developed a biomass gasification engineering with high gas efficiency and a high methane output which allows it to be used for gas-engine applications. This procedure has been given the name Milena, and the merchandise gas can be upgraded to SNG and ECN has the aspiration to turn this into big 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 non renewable ) so utilizing SNG for biomass would be a replacement for this and the biomass is available in big measures and it a batch cleaner and friendlier to the environment than natural gas.14
The biomass has to be converted into SNG by gasification and so methanation ( theses procedures and their lineations have been mentioned before ) . This allows it to make efficiency, say from wood, up to 65 % ( this efficiency is calculated from the chemical energy end product of SNG compared to the chemical energy input of wood ) . Biomass ( e.g. wood and straw ) being used to bring forth SNG has the advantage over coal based SNG of being about CO2 impersonal, without CCS. Production of man-made natural gas ( SNG ) from coal and dry biomass.4
The chief accelerators that are used as methanation accelerators are nickel or nickel supported accelerators. This is because the cardinal accelerator belongingss of Ni are first-class for methanation as it has long life, high activity, selectivity for the formation of methane in penchant to other hydrocarbons and the low cost compared to other accelerators. One of the chief disadvantages for nickel accelerators is the sensitiveness to toxic condition by sulfur, other accelerators are available that are sulphur-resistant and besides catalyse the methanation reaction but these are much less active than nickel ensuing in a slower rate of reaction.
For illustration, one maker ‘s accelerators are formulated on Ca aluminate base with the active Ni incorporated in a NiO/MgO solution, this leads to negligible nickel sintering.10In catalytic methanation many boosters for Nis have been studied such as Cu, Zn oxide, periclase, Fe, Ca oxide, chromia and aluminum oxide. What was found was that aluminum oxide, chromia and periclase were the best boosters in footings of activity and thermic stableness. It was besides found that for thermic and mechanical stableness “ the best of a figure of NiO methanation accelerators on supports of A12O3, a mixture of A12O3 and CaO, MgO, SiO2 and Cr2 O3 was NiO-AI2O3 incorporating 35 % NiO. “ 15 Many other factors are taken into consideration when taking the accelerator for the methanation procedure. These are explained below:
( I ) Sulphur toxic condition.
Sulphur toxic condition causes the methanation accelerators, to go inactive, this is because the reactants have brought in an foreigner molecule and this sits on the active site, the reactants now have to vie with this toxicant for the active sites and this consequences in a loss of the active surface country hence diminishing the rate of reaction.10
( two ) Thermal stableness.
This reaction is extremely exothermal it is really of import to do certain that the reaction temperature does non go excessively high because it affects the equilibrium province of the reaction unfavorably and the accelerator life lessenings due to sintering of the metal atoms, where the atoms come together, diminishing the surface country compared to when no sintering took topographic point, therefore less reaction is obtained. As mentioned antecedently the reaction temperature for this reaction is 300A°C-400A°Cfor which the Ni based accelerators used are sufficient in footings of length of service and activity. But there are accelerators cheapnesss are able to run at higher temperatures than Nis based accelerators and these would be even more desirable as “ the higher the temperature at which the heat of methanation is released the more efficaciously can it lend to overall thermic efficiency of the transition procedure, for illustration of coal to SNG, it is besides worthwhile to detect that at these higher temperatures the job of sulfur toxic condition lessenings due to instability of the accelerator metal sulphide9. So why is it that in industry the usage of accelerators that are suited for operation at higher temperatures are non selected and for e.g. nickel accelerators are favoured? This is due to the fact that it is non ever executable to utilize the best accelerator for the procedure as it may be excessively much to purchase.
( three ) Coke formation and fouling
Carbon in its unreactive signifier, or as Ni3C produced on the Nickel accelerator, causes a loss of accelerator activity9. The coke formed blocks the reactants from making the active sites and the fouling is caused by the reaction organizing a byproduct which so sits on the active site, dissembling it. It is possible to avoid the unwanted C formation in the industry of SNG by commanding the H2O gas displacement reaction. This is the second measure shown in figure 2 antecedently.
The cost of nickel accelerators varies as the monetary value of Ni fluctuates. The providers of these accelerators do non sell merely a few kgs of the accelerator they have a minimal orders measure, e.g. 20 dozenss at the rate of $ 15000- $ 30000 per ton. An illustration of a Methanation accelerator used in industry is the SG-9701 ( the name may be fancy but it is largely nickel as shown in the tabular array ) produced by the planetary leader in contact action, BASF who have found that although the accelerators operate at low temperature and demo good transition rates in the Methanation procedure, “ they finally begin to age and lose their effectivity ” , that is why through their current research they have identified that “ Methanation Catalyst relies on the mature combination of nickel oxide engineering on an alumina matrix. However, through careful control of composing and geometry and the add-on of a Rare Earth booster, a figure of public presentation betterments are achieved ” , these betterments are temperature opposition and long mechanical life. “ BASF ‘s methanation accelerator besides boasts a superior physical make-up cut downing impairment that can take to increased force per unit area bead in the system ” 16
For the hereafter?
Another SNG undertaking was decided upon in this April between ConocoPhillips and POSCO ( a Korean steel-manufacturing company ) in which ConocoPhillips ‘ E-Gas engineering is being used with POSCO ‘s Gwangyang coal to SNG undertaking. This installation has targeted production of 500,000 m.t. of SNG ; I will non travel farther with this undertaking as the methanation engineering to be used has non yet been announced and a new engineering to bring forth SNG utilizing crude oil coke ( petcoke ) ( an advanced engineering that captures and sequesters CO2 emanations from an industrial beginning ) is to be implemented with this at a farther phase. 12
Hydromethanation-Peabody Energy and GreatPoint Energy Mass late signed an understanding to bring forth SNG from coal, H2 from coal and besides CCS undertakings. These are wanted to be developed with Bluegas engineering, which “ uses catalytic Hydromethanation to bring forth H2 and SNG. The procedure is more efficient and cost effectual than conventional gasification paths to SNG ” . In the bluegas procedure a “ properness accelerator 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 organize CH4, CO2, H2 and CO. ” 12
There is besides a German-Austrian undertaking that wants to bring forth methane from excess electrical energy that has been generated from solar or wind power and a procedure that combines methanation with electrolysis has been developed at the Center for Solar Energy and Hydrogen Research, Germany.
Methanation is a really of import procedure particularly in today ‘s environment where we look to cut down CO2 emanations further and bring forthing SNG from biomass utilizing the methanation procedure does this instead than utilizing natural gas. Methane is used in the gas that provides our places with energy and warming. We need to happen even more efficient procedures like the 1s described above that usage methanation to bring forth SNG.