Encyclopedia of Environmental Science and Engineering, Volume I and II

FOSSIL FUEL CLEANING PROCESSES 421

The sulfur from a claus plant may be produced in vari-

ous forms, such as liquid, fl aked or prilled. Form of choice is

determined by transportation mode and end usage.

Dry bed absorption — catalytic conversion ( Haines

Process ) In the Haines Process (see Figure 9), sulfur is removed

from sour natural gas using zeolites or molecular seives.

Hydrogen sulfi de is absorbed from the gas on a bed of

zeolites until the bed becomes saturated with H 2 S. The bed is

then regenerated with hot SO 2 bearing gases, generated from

burning a part of the liquid sulfur production.

The zeolite catalyzes the reaction of H 2 S form sulfur

vapor. The regeneration effl uent gases are cooled and sulfur

is condensed.

Liquid media absorption — air oxidation Most com-

monly in use in Europe for removal and recovery of sulfur

from manufactured gases such as coal gas or coke oven gas,

several processes in this category are available today.

Typically, the process scheme involves absorption of

H 2 S in a slightly alkaline solution containing oxygen carri-

ers. Regeneration of the solution is by air oxidation. The H 2 S

is oxidized to elemental sulfur. Figure 10 shows the typical

processing scheme.

The air also acts as a fl otation agent for the sulfur which

is collected at the regenerated solution surface as a froth. The

sulfur sludge is either fi ltered or centrifuged to yield a sulfur

cake which may be recovered as a wet paste or dry powder.

Liquid media absorption — direct conversion ( Townsend

Process ) The Townsend Process is perhaps one of the newest

sulfur removal processes on the scene today. Still in forma-

tive stages of development, its potential advantages point to

it directly challenging the other conventional system con-

taining an amine plant, a dehydration plant and a claus sulfur

plant. The Townsend plant offers the added advantage of

recovering a higher percentage of the sulfur.

The Townsend Process uses an aqueous solution of an

organic solvent such as triethylene glycol to contact the sour

gas and simultaneously sweeten the gas, dehydrate the gas

and convert the gas to elemental sulfur.

ENVIRONMENTAL CONCERNS

Trowbridge^10 states that reductions in lead content of fuel oil

are occurring world wide. Unleaded mo gas originally intro-

duced in California in 1975 is now available throughout the

U.S., where permissible maximum lead levels were estab-

lished at 0.1 grams/gal after 1986. Trowbridge describes

additional environmental concerns and fuel treatment proce-

dures which are summarized below:

• ozone formation—reduction of gasoline vapor
  pressure


• carbon monoxide emissions—add oxygenates to
  blend


• benzene emissions—reduce fraction in reformate
  by extraction for example.

DESULFURIZATION OF COAL

Although coal buring accounts for only about 1/4 of the

nation’s energy, approximately 2/3 of all the sulfur dioxide

emitted in the United States is traceable to its usage. And

since coal supplies far outstrip gas and oil reserves, interest

in coal desulfurization is great.

Presently, however, there are no processes suffi ciently

developed, either technically or commercially, which have any

signifi cant impact on the industry. The following is, therefore,

SWEET GAS

SOUR GAS

LEGEND

RICH SOLUTION

LEAN

SOLUTION

FILTRATE

AIR

SULFUR FROTH

LIQUID MEDIA ABSORPTION

A R F

SK

A - ABSORBER

R - REGENERATOR

SK - SKIM TANK

F - FILTER

SULFUR CAKE

FIGURE 10

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