Hydrogen requirement to shift thermal coal to syncrude

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Contents 1 Question 2 Answer 3 Workings 4 Description

Question

How much hydrogen and Thermal Coal is theoretically required to produce 25GL of syncrude?

Answer

15,647 GL of hydrogen and 26.75 MegaTonnes of Thermal Coal.

Workings

Terms	Basis	Unit	Value
target H gm-atom/C gm-atom		gm-atom/gm-atom	1.60
annual production volume		GL per annum	25.00
average specific gravity		gm/ml	0.80
net available H on a N- and S-free basis	dmmf	gm-atom/gm-atom	0.65
feed of CHα/gm-atom C	dmmf	gm/gm-atom	12.66
required H2/C in the CHα reduction reaction	dmmf	m/gm-atom	0.48
required H2/C in the CHα reduction reaction (@STP)	dmmf	L/gm-atom	10.66
output from reduction reaction/gm-atom C	dmmf	gm/gm-atom	13.62
output from reduction reaction/gm-atom C	dmmf	ml/gm-atom	17.03
gm-atom C/unit volume of liquid product	dmmf	gm-atom/ml	0.06
feed/gm-atom C	dmmf	gm/gm-atom	14.03
feed/gm-atom C	mf	gm/gm-atom	14.68
feed/gm-atom C	ar	gm/gm-atom	18.22
gm-atom C required for annual liquid production	mmf	gm-atom	1.47E+12
Coal required per annum	ar	mtonne per annum	26.75
Hydrogen required per annum		mtonne per annum	1.408
Hydrogen required per annum		GL	15,647
Hydrogen required per annum		million cu. m.	15,647

Description

The Proximate Analysis of coal frequently serves as the basis for contracts and specifications. Four groups of constituents are determined as follows:

• free moisture, the sum of water held at the surface of coal particles;
• the hydroscopic moisture held within the coal particle;
• the combustible matter, volatile matter and fixed carbon; and,
• ash.

The analytical basis for performing calculations on raw feed coal – ‘Run of Mine (ROM) coal, which has undergone some preliminary treatment in the form (generally) of classification – is referred to as ‘As-received’. An Ultimate Analysis reports the presence of the major chemical elements as weight fractions:

• carbon (C);
• hydrogen (H), present as H₂,
• oxygen (O), present as O₂;
• nitrogen (N), present as N₂; and,
• sulphur (S), in its organic form.

For the purpose of preliminary estimation of the net hydrogen in coal, available for oxidation in combustion and gasification processes, or for participation as a reductant in liquefaction processes, account of the oxygen in coal may be made by considering it to be in combination with hydrogen as ‘combined water’. When stated on a dry, mineral matter-free (dmmf) basis, the Ultimate Analysis reports the chemical components of the combustible coal. Conversion from the ‘As-received’ basis to the dmmf basis is effected through the following calculations:

Equations of a form similar to those shown above convert the nitrogen and sulphur bases. The elemental hydrogen and oxygen compositions, relative to the carbon content of the coal, may be computed as follows:

The molar hydrogen content, relative to the carbon content of the coal, may be computed by dividing the elemental hydrogen content by two. The net availability of hydrogen, as H2, for oxidation in combustion and gasification, and as a reductant in liquefaction processes, on a N- and S- free and dmmf basis, is computed as follows:

A Thermal Coal with the Ultimate Analysis (as received) shown in the table below may be represented on a N- and S-free, dry mineral matter-free (dmmf) basis as CH0.65.

• C 65.93%
• Available H2 3.50%
• N2 1.30%
• S 0.00%
• Combined water 6.31%
• Free moisture 4.38%
• ash (as weighed) 18.58%

 The stoichiometric hydrogen requirement to shift a coal, represented as a hydrocarbon of the general formula, CHα, to a hydrocarbon liquid of the general formula, CHβ, is expressed by the reaction equation:

0.476 gm-moles of H2 per gm-atom of carbon are theoretically required for a shift from α = 0.65 to β = 1.6. On the basis that 1 gm-mole of H2 occupies 22.4 Litres at Standard conditions of Temperature and Pressure (STP), 10.66 Litres of H2 are required per gm-atom of carbon consumed. The theoretical hydrogen requirement associated with the production of a certain amount of liquid hydrocarbon product proceeds as follows:

1. The quantity of liquid produced per gram-atom of carbon consumed corresponds to the molecular weight of the product hydrocarbon.
2. The volumetric production of liquid per gram-atom of carbon consumed is computed by dividing by the average density of the product (a value of 0.80 gm/millilitre may be assumed).
3. Inversion provides the quantity of gm-atoms of carbon consumed to achieve the volumetric production.
4. Multiplying the molar hydrogen requirement per gm-atoms of carbon by the molecular weight of hydrogen and then multiplying by the gm-atoms of carbon consumed yields the mass requirement of hydrogen.
5. Multiplying the volumetric hydrogen requirement per gm-atoms of carbon consumed by the gm-atoms of carbon consumed yields the total volumetric requirement of hydrogen.

The theoretical coal requirement associated with the production of a certain amount of liquid hydrocarbon product proceeds as follows:

1. The coal feed rate/gm atom of carbon fed, on a dmmf basis, is computed by summing the product of each elemental composition, expressed as gm-atom/gm-atom C and its respective atomic weight.
2. The coal feed rate/gm atom of carbon fed, on a moist, mineral matter-free (mmmf) basis – that is, coal is free of mineral matter, but account is taken of its free moisture content – is computed by dividing the theoretical coal requirement on a dmmf basis by one minus the free moisture content, expressed as a weight fraction.
3. The coal feed rate/gm atom of carbon fed, on an as- received (ar) basis, is computed by dividing the theoretical coal requirement on a dmmf basis by one minus the sum of the free moisture and ash contents, expressed as a weight fractions.
4. The coal feed rate/gm atom of carbon fed, on an as-received (ar) basis, is multiplied by the quantity of gm-atoms of carbon consumed to achieve the volumetric production.

The theoretical feedstock requirement to produce 25 GL of a ‘nominal’ synthetic crude with the hydrocarbon formula CH1.6 from coal with this composition is approximately 27 million tonnes per annum. The shift in H/C ratio from 0.65 to 1.6 requires a theoretical amount of hydrogen of approximately 1.4 million tonnes, corresponding to approximately 15.60 billion cubic metres at Standard Conditions of Temperature and Pressure (STP). (This corresponds to about 3% of the global production of Hydrogen in 2004.)