Encyclopedia of Environmental Science and Engineering, Volume I and II

422 FOSSIL FUEL CLEANING PROCESSES

a brief summary of the more pertinent processes currently

under evaluation.

A typical high-sulfur, bituminous coal (4.9%) sulfur may

be characterized by the composition shown in Table 4.

The solvent refi ne process Solvent refi ned coal (SRC) is

one name among others given to a reconstituted coal which

has been dissolved, fi ltered, and separated from its solvent.

It is free of water, low in sulfur, very low in ash, and suffi -

ciently low in melting point that it can be handled as a fl uid.

In the process (see Figure 11), coal is ground to 80%

through a 200 mesh screen and slurried in an initial solvent

oil. The slurry is pumped to a pressure of 1,000 lb/sq.in. and

passed upwards through a heater to bring the slurry to a tem-

perature of 45C.

The fl ow rate is between a half and one space velocity. As

the material leaves the heater, more than 90% of the carbon

in the coal is in solution. (Anthracite coal is an exception.)

A small amount of hydrogen is introduced into the slurry

prior to preheating. The hydrogen prevents repolymerization

of the dissolved coal. A portion of the organic sulfur in the coal

unites with hydrogen to form hydrogen sulphide, which is later

separated as a gas. The unutilized hydrogen is recycled back to

the preheater. After the coal has been dissolved, the ash is fi l-

tered at a pressure of about 50 lb/sq.in. The pyritic sulfur leaves

the process mixed with the other separated mineral matter.

The fi ltrate or coal solution, now greatly reduced in ash

and sulfur is fl ash evaporated to obtain the necessary recycle

solvent. It has been demonstrated that no make up solvent

is required. In fact, an excess of solvent oil, released from

the coal structure itself during solvation is recoverable, if

desired. The remaining hot liquid residue is discharged and

cooled to form a hard, brittle solid of solvent refi ned coal.

Table 5 shows a comparative analysis of a raw coal (%

S—3.27%) and the solvent refi ned process, along with rough

economies.

Obviously, solvent refi ned coal represents a marked

improvement over the raw starting material. Sulfur content is

reduced by about 30%, Ash content by 93% and heating value

(in BTU/LB) is signifi cantly increased. However, the cost of

these improvements produces a fuel whose cost is higher than

low sulfur oil.

Devolatilization I carbonization to a low sulfur char

United Engineers and Company have investigated the use

of a fl uidized bed desulfurization process. Figure 12 shows

general fl ow scheme for the label scale process.

ASH PRODUCTS

ASH PROCESSING

ASH RESIDUE

FILTER

DISSOLVER

PREHEATER

FEED PUMP

COAL SOLVENT

SLURRY

TA N K

HYDROGEN

GAS TREATMENT

DISTILLATION

LIGHT OIL

FLASH EVAPORATOR

SOLVENT

REFINED COAL

SOLVENT REFINE COAL PROCESS

FIGURE 11

TABLE 4

Coal Analysis (on dry basis)

Volatile combustible matter 42%

Ash 10%

Fixed carbon 48%

Moisture —

Sulfur breakdown (by % —forms available)

Sulfate 0.33

Pyritic 2.53

Organic 2.04

4.9%

TABLE 5

Raw coal Solvent refi ned coal

Ash 6.91% 0.41

Carbon 71.31 89.18

Sulfur 3.27 0.95

Volatile matter 44.00 51.00

Heat content (BTU/LB) 13978 15956

Cost ($/Ton) 40.00 120.00

Cost (c/MMBTU) 156.00 469.00

NITROGEN

AIR

STEAM

GAS VENT

FLUIDIZED AND DESULFURIZATION

FIGURE 12

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