30-09-2016, 11:38 AM
Overview on production and utilisation of di-methyl ether as sustainable fuel for clean energy production
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ABSTRACT:-
Dimethyl ether(DME) has characteristics similar to liquefied petroleum gas(LPG) as a household cooking fuel. As such, DME is an attractive fuel for clean cooking. DME can be made from any carbonaceous feedstock, including natural gas, coal, or biomass, using established technologies. This article reviews characteristics of DME and technology for making DME from coal. DME is the simplest ether. It is a colorless gas at ambient temperature and pressure, with a slight odour. It is used as an aerosol propellant in hair sprays and other personal care. DME is manufactured today in small-scale facilities by catalytic dehydration of methanol, with methanol typically made from natural gas. Technologies are available for making DME more directly from carbonaceous fuels without an intermediate step of methanol production, but the small size of today’s DME markets have not justified building direct conversion facilities. Synthesis of DME from syngas is similar in many respects to synthesis of methanol, an established commercial process. Methanol is synthesized over a copper based catalyst (eg., CuO/ZnO).As the demand for clean cooking fuel grows in the future , the fraction of LPG that we import will also grow , because our domestic oil and natural gas resources are limited. DME has properties similar to LPG as a cooking fuel, and DME is potentially much more widely available than LPG because it is manufactured from coal. For coal derived DME to become viable commercial household fuel will require successful demonstration of the production, distribution, and utilization of DME. The most economical approach in making DME from coal will be at facilities using “once through” process designs that produce DME and an electricity co-product. With co-production of DME and electricity, there would be significant savings in primary coal needed to meet a given demand for cooking energy services plus electricity.
INTRODUCTION:-
With the developing technology and promotion of mankind we are depleting the natural resources and polluting the environment to the core. The major pollution to the environment is production of energy. Coal is the worst offender that produces 80% of all power plant emissions. Nuclear power plants produce no global warming or air pollution but can cause catastrophic damage to human health. To reduce pollution we have to produce clean energy.What is clean energy? Clean energy is nothing but generating no pollution or emissions How to obtain clean energy? The one form of clean energy that is trending now is energy from dimethylether(DME). DME isconsidered as 21-st century energy. DME is produced from renewable materials like biomass , waste and agricultural products. DME is gaseous at normal temperature and pressure. Liquid at modest pressure and cooling. DME has received approval for legal use as vehicle fuel in California. The topic we are going to discuss is about production and utilisation of DME.
DIMETHYL ETHER:-
Dimethyl ether (DME), also known as methoxymethane, is the organic compound with the formula CH3OCH3, simplified to C2H6O. The simplest ether, it is acolorless gas that is a useful precursor to other organic compounds and an aerosol propellant and is being studied as a future energy option. Itisan isomer of ethanol.
BOILING POINT= -24ºC
MELTING POINT=-141ºC
PRODUCTION:-
Dimethyetheris produced in two ways
1) From methanol.
2) From coal.
FROM METHANOL:-
DME is produced from methanol by catalytic dehydration in small scale industries. Catalysts used are CuO / ZnO / Al2O3. The reactions involved are
CO + 2H2 → CH3OH
2CH3OH → CH3OCH3 + H2O
By combining some methanol and dehydration catalyst in same reactors the reactions can proceed simultaneously resulting in direct synthesis of Dimethy ether(DME). The water gas shift is also involved, since methanol catalyst is also an effective water-gas-shift catalyst.
H2O + CO → H2 + CO2
The essential operations in the process are the preheating of the raw material (nearly pure methanol), reacting methanol to form DME, product separation, contaminant separation, and methanol separation and recycle. Crude methanol, containing about 2 mol % impurities, is fed as a liquid in Stream1, pumped up to 16.8 atm and combined with Stream 19, a methanol recycle stream. Stream 4 is then sent into heat exchanger E-101 where it is heated to a temperature of 250°C before it is sent to a packed bed reactor, R-101, to form DME .The reaction is slightly exothermic and the reaction products are heated to approximately 365°C before leaving the reactor. The reactor effluent is cooled in E-102 and then throttled to 10 atm before entering T-101. Here, the dimethyl ether is separated from the other components as distillate, Stream 9. The bottom product, Stream 10, is throttled to 6.9 atm and sent to T-102 where the methanol and water are separated from the waste components. The waste components exit as distillate, Stream 12, and are sent to a waste treatment facility. The waterand methanol exit as the bottoms stream, Stream 13. This stream is then throttled to 1 atm and then sent to T-103 where the water and methanol are separated .The water exits the bottom of the distillation column as Stream 15, and is sent to waste treatment. The methanol exits the column as distillate, Stream 16. Stream 16 is then pumped up to 16.8 atmand recycled back to mix with fresh methanol, Stream 3 in vessel.
OTHER NOVEL METHODS TO PRODUCE DME:-
• In 2013, Jamshidi et al proposed thatME can be produced by dehydration reaction of methanol by using solid catalysts in catalytic reactions. This study shows an analysis of the performance of Al62,2Cu25,5Fe12,3 quasi crystalline alloy as catalyst for dehydrating methanol to produce DME. These quasi crystalline alloys are stable at high temperatures, show a low thermal conductivity and exhibit a fragile nature, which turn them to be easily crushed. Also, their activity is not affected by water
2. FROM COAL:-
The production of dimethyl ether(DME) from coal has been proposed by LARSON and REN in 2003 for large scale production of DME.
In this process coal is first gasified in oxygen to produce a raw synthesis gas containing primarily hydrogen and carbon monoxide. The gas is cooled and cleaned before having its H2:CO ratio adjusted in a water-gas-shift reactor to an optimum value for subsequent catalytic synthesis of DME. Because the H2/CO ratio of synthesis gas obtained by the coal gasification ranges from 0.5 to 1.0, the gas composition is adjusted by the shift reaction so that H2/CO = 1, and it is then supplied for DME synthesis. In this synthesis step where the reaction (H2/CO=1) is achieved, the difference of H2COratio to be adjusted is so narrow in comparison with the reaction(d) (H2/CO=2) that the equipment size and utility consumption for the shift conversion step are smaller. The effluent from the slurry reactor is cooled and chilled in order to separate the liquid phase ( DME , CO2 and small amount of methanol and water) from the gaseous phase containing unreacted H2 and CO. Most of the separated gas is recycled to the reactor. Because the one-through reaction rate is high, the recycle ratio is sufficient at 1:l. After C02 removal, the product DME is natural gas, it can be converted to synthesis gas of H2CO = 1 by means of C02 reforming and used to the DME synthesis.
Other novel methods for production of coal:-
K.B. Kabir et al, proposed a steady state model for DME synthesis from Victorian brown coal has been developed integrating key processes – drying, gasification, and the synthesis. Influence of various process parameters on the process performance has been evaluated. The results shed insights into the research needs for development of the DME synthesis process using Victorian brown coal. Victorian brown coal is low in sulphur content. Syngas from Victorian brown coal has low concentration of sulphur containing gases. On the other hand, HCN and HCl concentration in the Victorian brown coal syngas is usually higher than that of other coals. It is well known that cleaning of syngas is necessary to avoid poisoning of methanol synthesis catalysts. Preliminary experiments indicate that more extensive study on gasification and water gas shift is necessary to optimize the syngas composition for DME synthesis. Therefore, work on appropriate gasification and water gas shift catalysts will be performed.Another important aspect is the catalyst for syngas to DME conversion.
UTILISATION OF DIMETHYL ETHER:-
Dimethyl ether(DME) is used as substitute for diesel fuel; transport fuel; power generation fuel; domestic gas.
DME ASDIESEL FUEL :-
Since the mid 1990’s dimethyl ether (cetane: #55–60) has been promoted as a diesel substitute (cetane: #55) .With the concerns of diminishing petroleum
reserves, dimethyl ether is garnering more attention as a viable alternative to diesel. The advantages of dimethyl ether over conventional diesel include decreased emissions ofNOx, hydrocarbons and carbon monoxide. Dimethyl ether combustion does not produce soot. CIDI engine tests have been performed with diesel and dimethyl ether in order to compare the exhaust emissions . The decreased pollutant emissions observed with dimethyl ether will contribute to cleaner air (i.e., no smog). Dimethyl etherfueledCIDI engines are also quieter than conventional diesels. The operation of a DME engine requires a new storage system and a new fuel delivery system both have been addressed. The engine itself does not need modification. However, in order to achieve an equivalent driving range as that of a CIDI diesel, a DME fuel storage tank must be twice the size of a conventional diesel fuel tank due to the lower energy density of DME compared with diesel fuel. The most challenging aspects of aDMEengine are related to its physical properties and not to its combustion characteristics. The viscosity of DME is lower than that of diesel by a factor of about 20; causing an increased amount of leakage in pumps and fuel injectors. There are also lubrication issues with DME; resulting in premature wear and eventual failure of pumps and fuel injectors. Additives have been used to increase the lubricityof DME, and the commonly used additives have been those developed for reformulated diesel Fundamental research onimproving DME wearand lubricity isongoing
This utilisation was presented as at PETROTECH-2001 conference, NEWDELHI, INDIA, January 2001 by Dr.ArunBasu, senior engineer, technology commercialization and Mr. John .M. Wainwright. A new , ultra clean fuel for gas turbines a blend consisting primarily of dimethyl ether with lesser amounts of methanol and water- has been identified by BP Amoco. High purity DME is currently used as an aerosol propellant due to its aerosol environmentally benign characteristics. BP Amoco initiated key programs to test combustors ith equivalent electricity production of nearly 20 MW. Later BP Amoco collabrated with Electric Power Development Corporation, Japan to conduct additional follow up tests. These tests show that DME is an excellent gas turbine fuel with emissions properties comparable to natural gas. Based on the results combustion test progaram, GE Energy systems is prepared to pursue commercial offers of DME- fired E-class and F-class heavy duty gas turbines.
PERFORMANCE IN GAS TURBINES: As DME can be totally vapourized quite effectively at inlet conditions (eg., at 150-250 psig) of gas turbine combustors, it can be used in modern efficient dry-low NOX emissions at 25 ppmvd (at 15% oxygen level). Liquid DME is stored as either refrigerated liquid or under pressure (at ambient temperature) can be first pumped to a higher pressure and vapourized by the utilization of hot water/steam produced as a part of the combined cycle power plant. For handling of DME specific industrially proven materials for gaskets/ seals will be used.
Therefore DME is a promising new gas turbine fuel. Their results show that using refridgerated DME at minus 25C would be about 1.6% lower than that using natural gas and about 6.3% lower than that using light naphtha.
DME AS DOMESTIC GAS:-
DME is produced globally today at a rate of about 150,000 t per year [Naqvi, 2002], but this production level will increase dramatically in the near future. Construction of a DME plant with capacity of 110,000 t/yrwascompleted in early 2005 in Sichuan Province [Toyo, 2004]. Natural gaswas the feedstock. In 2002, China’s State Development Planning Commission approved plans for the first large-scale coal-to-DME project. The first phase had a capacity of 210,000 t per year, and the second phase would have a capacity of 630,000 t per year.Other DME projects are also under development in China. Theprojects are targeting household cooking as the primary end-use for the DME. In addition to the Chinese projects, an 800,000 t per year DME – fromnatural gas facilityhad come on line in Iran in 2006 [HaldorTopsoe, 2004]. Most of the DME product from this facility will be used as an LPG substitute. DME is relatively inert, non-corrosive, non-carcinogenic,almost non-toxic, and does not form peroxides by prolongedexposure to air [Hansen et al., 1995]. It requiresmild pressurization similarto that required for LPG to bestored as a liquid. It has a volumetric energy density asa liquid about 80 % of that of propane, a major constituentof LPG. Table 2compares some physical properties of DME with those of the main constituents of LPG. DME burns with a clean blue flame over a wide range of air/fuelratios [Fleisch et al., 1995; ICC, 2003]. Han et al. [2004]discuss emissions associated with DME cooking, and Bizzo et al. [2004] briefly discuss DME-related safety issues.As the demand for clean cooking fuel grows in the futurein China, the fraction of LPG that China imports will alsogrow, because China’s domestic oil and natural gas resourcesare limited. ImportedLPG prices track internationaloil prices, so, as oil pricesrise in the future,importing LPG will become an increasingly expensiveproposition for China. Moreover, as Chinese LPG demand grows, global competition for available supplies of LPG will intensify, ultimately contributing to higher international LPG prices. High LPG prices will limit the extent to which imported LPG can meet China’s domestic needs, especially the needsof inland provinces where addedtransportation costs are involved. DME has properties very similar to LPG as a cooking fuel, and DME is potentially much more widely availablethan LPG in China because it can be manufactured fromcoal. The analysis in this paper suggests that coal-derived DME in China could be competitive in many regions ofChina with imported LPG even at relatively modest world oil prices.
DME, hydrogen, and fuel cells:-
There are four processes for generating hydrogen-richfuel-cell feeds from hydrocarbon fuels: decomposition, steam reforming, partial oxidation, and autothermal reforming.
Decomposition and partialoxidation result in high yields of carbon monoxide and are generally not suited for fuel cell applications owing to their lower efficiencies as comparedto the other reforming techniques. Steam reforming produces the highest hydrogen yield with the leastamount of carbon monoxide. The shortcoming of steam reforming is that the process is inherently endothermic and hence requires longer start-up times. For manytransportationapplications, the start-up time is critical for consumer acceptance. Autothermal reforming combines the endothermic steam reforming reaction with the exothermic partial oxidationreaction. Intrinsically, autothermal processing has decreased start-up times and a fasterresponse to a change in load thanthe other processes.However, the reformate from auto thermal processing has a lower hydrogen concentration than steam reforming. Methane, methanol, ethanol, and gasoline are the most widely researched fuels for automotive fuel cells
Methane, ethanol, and gasolineall require high temperatureautothermal processing (>700◦C). Ethanol and gasoline tend to form carbon resulting in durabilityissues. Carbonformation can be suppressed with the addition of water,Fig. 9. Plot of the difference in thermodynamic equilibrium product molefractions of hydrogen and carbon monoxide on a wet basis as a function ofsteam-to-carbon ratio and temperature for dimethyl ether steam reforming.Data reproduced from referencebut for realistic conditions (i.e., 1.2 < S/C < 1.5) carbon formationremains a critical challenge. Methanol is a low temperature (∼280 ◦C) reforming fuel that exhibitshigh carbon dioxideselectivities (>98%), and high hydrogen yields (>70%). Thermodynamically, the processing of dimethyl ether withsteam indicates the complete conversion of dimethyl etherto hydrogen, carbon monoxide, and carbon dioxide.Fig. 9 shows the optimal conditions for producing the largest amount of hydrogen, while minimizing the amount of carbonmonoxide. The global maximum occursat a steam-to-carbonratio of 1.50 and a temperature of 200 ◦C.Dimethyl ether steam reforming occurs via a two stepreactionsequence. The first step is the conversionof dimethyl ether to methanol via DME hydrolysis, followedby methanol steam reforming over Cu or Cu/ZnO
Conclusions:-
Current transportationfuels are based on petroleum, aresource that is being depleted, and whose importation has political and societal ramifications. Hydrogen isviewed by many as the ultimate ‘end-game’ fuel. A transition from petroleum to DME to hydrogen may be more cost effectivethan a step change to hydrogen. DME can be introduced and exploited with existing technologies, and enable the eventual implementation of advanced technologies, such as fuel cells. Because dimethyl ether is produced from natural gas, coal, or biomass, dimethyl ether canincrease the energy security ofthe US by displacing petroleum derived fuels. The prominentadvantages of dimethylether as a fuel and energy carrierareimethyl ether can be used in the most efficient engine technology currently produced (i.e., CIDI). Dimethyl ether demonstrated lower NOxand SOxthan conventional diesel; is sootless.Dimethyl ether can be used as a residential fuel for heating and cooking.Dimethyl ether as a turbine fuel demonstrates an increase in efficiency, and decreased NOxand CO compared to methane and liquid naptha.On-board automotive fuel processors using methanol and dimethyl ether exhibit the lowest start-up energies and the lowest fuel processor volumes—correlating to higher overall efficiencies as compared to ethanol, methane, and gasoline fueled fuel processor fuel cell vehicles.Dimethyl ether can produce hydrogen-rich fuel-cell feeds with hydrogen yields equivalent to those of methanol at comparable operating temperatures.The infrastructure of dimethyl ether is less cost intensive than that for hydrogen because dimethyl ether can use the existing LPG and natural gas infrastructures for transport and storage.Dimethyl ether is non-toxic, non-tetra genic, non - mutagenic, and non-carcinogenic.Dimethyl ether has a global warming potential of 0.1 (cf., 1.0 for CO2) for a 500-year time horizon. Hydrogen fuel cells show unprecedented efficiencies, but with the current technical challenges of hydrogen storage,hydrogen production efficiencies, fuel cell durability, high infrastructure costs, and high fuel cell costs, there is little likelihood that automotive fuel cell systems will significantly penetrate the commercial market in the near future.