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SAJJAD KHUDHUR ABBASChemical Engineering , Al-Muthanna University, IraqOil & Gas Safety and Health Professional OSHACADEMYTrainer of Trainers (TOT) - Canadian Center of Human Development Episode 3 : Production of Synthesis Gas by Steam Methane Reforming

History of Synthesis GasIn 1780, Felice Fontana discovered that combustible gas develops if water vapor is passed over carbon at temperatures over 500 C. This CO and H2 containing gas was called water gas and mainly used for lighting purposes in the19th century.

As of the beginning of the 20th century, H2/CO-mixtures were used for syntheses of hydrocarbons and then, as a consequence, also called synthesis gas.

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Haber and Bosch discovered the synthesis of ammonia from H2 and N2 in 1910 and the first industrial ammonia synthesis plant was commissioned in 1913. The production of liquid hydrocarbons and oxygenates from syngas conversion over iron catalysts was discovered in 1923 by Fischer and Tropsch.Much of the syngas conversion processes were being developed in Germany during the first and second world wars at a time when natural resources were becoming scare and alternative routes for hydrogen production, ammonia synthesis, and transportation fuels were a necessity. In 1943/44, this was applied for large-scale production of artificial fuels from synthesis gas in Germany.

To this day, however, methanol and ammonia are still produced from syngas using essentially the same processes originally developed and, apart from hydrogen production, constitute the major uses of syngas.

What is synthesis gas ?

In its simplest form,syngas(also calledproducer gas, town gas, blue water gas, andsynthesis gas) is composed of carbon monoxide (CO) and hydrogen (H2). The name comes from its use.Syngas is combustible and often used as a fuel of internal combustion engines. It has less than half the energy density of natural gas.

syngas can be produced from any hydrocarbon feedstock, including: natural gas, naphtha, residual oil, petroleum coke, and coal.The lowest cost routes for syngas production, however, are based on natural gas, the cheapest option.The choice of technology for syngas production also depends on the scale of the synthesis operation.

Syngas production from solid fuels can require an even greater capital investment with the addition of feedstock handling and more complex syngas purification operations.The syngas composition, most importantly the H2/CO ratio, varies as a function of production technology and feedstock.Steam methane reforming yields H2/CO ratios of 3/1, while coal gasification yields ratios closer to unity or lower.

Physical Properties of Hydrogen (H2):With only one proton and one electron, hydrogen is the lightest of all chemical elements. At ambient temperature, molecular hydrogen, H2, is a colourless and odorless gas.hydrogen condenses to a colorless liquid, it freezes at 259.15 C.H2 is14 times lighter than air.

ValueUnitproperty2.016g mol1Molar mass898J mol1Heat of vaporizationProperties at 273.15 K, 101.3 kPa0.0899kg m3Density0.1645W m1 K1Thermal conductivityCp = 22.0, Cv = 6.51J mol1 K1Molar heat

ValueUnitProperty Boiling point (101.3 kPa)20.37KTemperature70.00kg m3Density (liquid)1.319kg m3Density (gas)Liquid at boiling point (101.3 kPa)Cp = 22.0, Cv = 6.51J mol1 K1Molar heat7918J mol1Enthalpy0.117W m1 K1Thermal conductivityGas at boiling point (101.3 kPa)Cp = 23.49, Cv = 12.8J mol1 K1Specific heatcapacity7020J mol1Enthalpy0.0185W m1 K1Thermal conductivityCritical Point33.00KTemperature1339kPaPressure30.09kg m3Density

Chemical properties of hydrogen

In air, H2 combusts to water with a hardly visible, weakly bluish flame. Hydrogen combines with almost any other element. Metal compounds with negatively charged hydrogen are called metal hydrides (e.g. CaH2, NaH, LiH).Hydrogen has a reducing effect on a lot of metal oxides when heated. Thus CuO with H2, for example, reacts to Cu and H2O. Hydrogen has a reducingeffect on a lot of metal oxides when heated.

Physical and Chemical Properties of Carbon Monoxide (CO):Carbon monoxide is colourless, odourless and tasteless. It is highly toxic,poorly soluble in water (solubility: 23 mL L1 at 20 C and 1 bar).

ValueUnitProperty28.010g mol1Molar mass10.9 76% Volume fractionExplosion range (in air at 101.3 kPa)Properties at 273.15 K, 101.3 kPa1.250kg m3DensityCp = 29.05,Cv = 20.68J mol1 K1Molar heat0.02324W m1 K1Thermal conductivity

ValueUnitPropertyBoiling point (101.3 kPa)81.65KTemperatureMelting point (101.3 kPa)74.15KTemperatureCritical point132.29KTemperature3496KpaPressure301kg m3Density

Chemical properties of CO

Together with air, carbon monoxide forms explosive mixtures in the concentration range of a CO-volume fraction of (10.9-76%).In engineering, it is obtained by separation from synthesis gas.The reason for its toxicity is its property to displace the oxygen from the hemoglobin-complex of blood, since the affinity of hemoglobin (Hb) to CO is about 300 times higher than to O2. The hemoglobin of a heavy smoker of cigarettes can reach a CO-saturation of up to 15% in the course of a day.

Uses of syngas

Syngas can be used to produce a variety of chemicals like ammonia and methanol. Syngas itself can be used as a fuel in internal combustion engine.Syngas is also used as an intermediate in producing synthetic petroleum for use as a fuel or lubricant via the FischerTropsch process and previously the Mobil methanol to gasoline process. syngas can be used to produce organic molecules such as synthetic natural gas (SNG-methane).

At these days, synthesis gas is mainly used for production of the products listed:

UsesProductAmmoniaH2 and N2Formic acidCOAcetic acidH2 and COMethanolMixtures of (H2, CO and CO2)

Production of Synthesis Gas from Hydrocarbons:In the production of synthesis gases from hydrocarbons, the components hydrogen and carbon monoxide usually appear as complementary products, carbon dioxide can be obtained as a by-product.

There are Several Methods to Production the Synthesis Gas from Hydrocarbons :Steam ReformingPartial Oxidation (PO ).Autothermal Reforming ( ATR).

The Process Selection depends on Two factors:The desired product composition (H2/CO ratio ).The feedstock available like natural gas, residual gases from refineries,LPG(Liquefied Petroleum Gas), naphtha, heavy oils, distillation residues, pitch and coal.The selected process in this project is Production Synthesis Gas by steam reforming of Methane Gas due to ratio (H2/CO)is equal to 3/1 and the feed is methane gas. the economic cost of the steam must be taken into account

The Advantages of (SMR):Steam reforming of natural gas are :

EfficientEconomicalwidely used process for hydrogen and monoxide productionprovides near- and mid-term energy security and environmental benefitsThe SMR produces a H2/CO ratio equal to three

We choose methane as a feed because of :

Methane is a wide distribution in nature.cheapMake a Less problems with the reformer.Make a longer age for reformer than other feed stockes.

MethaneMethane is achemical compoundwith thechemical formulaCH4(one atom ofcarbonand four atoms ofhydrogen). It is the simplestalkaneand the main component ofnatural gas.Methane is a colorless, odorless gas with a wide distribution in nature. It is the principal component of natural gas, a mixture containing about 75% CH4, 15% ethane (C2H6), and 5% other hydrocarbons, such as propane (C3H8) and butane (C4H10).ValueUnitPropertyCH4Molecular formula 16.04g mol-1Molar Mass0.656g cm-3Density at 25 C , 1 atm0.142mPa.sViscosity at -170 C5.34J g-1 k-1Specific heat capacity at -100 C-182 CMelting point 43.4cm s-1Flame Velocity

Critical Values- 82.5CTemperature 4.67MPaPressure0.162g cm-3Density

Sources of Methane

Natural sources

WetlandsOceansGeological sourcesWild animalsWildfires

Non Natural sources (Artificiality)Oil and Gas SystemLandfillsWastewaterCoal MinesAgriculture

Steam Reforming (Tubular Reforming)

Steam Reforming Methane (SMR) has been used for several decades since it has been developed in 1926 and over the years substantial improvements have been introduced. SMR process consists of gas feed pre-heating and pre-treatment, reforming.Steam reforming of methane is the main industrial route to produce synthesis gas (a mixture of hydrogen and carbon monoxide).In the steam reforming process, a light hydrocarbon feedstock (such as natural gas, refinery gas, LNG, or naphtha) is reacted with steam at elevated temperatures(typically 700 C to 900 C), and elevated pressures (15 to 30 bar) in nickel-based catalyst filled tubes to produce a synthesis gas. This gas consists primarily of hydrogen and carbon monoxide. , but other gases such as carbon dioxide and nitrogen, as well as water vapor are also present.The typical steam to carbon ratio falls in the range of (2.8 to 3.2 to 1).

steam reforming (SR) is highly endothermic and it is carried out at high temperature (700 - 900 C) and at pressures between 15 and 30 bar.

The standard enthalpies of reaction (at 298 K) are given in brackets. The most important reactions in steam reforming (SR) of methane are:

1. CH4(g) + H2O(g) CO(g) + 3H2(g) (H = +206 kJ/mol)

2. CO(g) + H2O(g) CO2(g) + H2(g) (H = -41 kJ/mol)

Reactions and thermodynamics

CatalystAll tubular reformers use catalyst inside the tubes in order to reduce the operating temperature. This is important in order to reduce the tube stresses resulting from high pressure and high temperatures The Ni-catalyst is needed since methane is a very thermodynamically stable molecule even at high temperatures. nickel catalyst filled tubes to produce a synthesis gas.Ni-catalyst is often in the form of thick-walled Raschig rings, with 16 mm in diameter and height, and a 6 8 mm hole in the middle.

Challenges

During the production of Synthesis gas, CO2 is also produced. The SMR process in centralized plants emits more than twice the CO2 than hydrogen produced. To avoid emission of CO2 into the atmosphere, CO2 can be concentrated, captured, and sequestered.

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