DEEP WELL INJECTION OF INDUSTRIAL WASTES:
A STATE-OF-THE-ART CASE HISTORY
W. A. Coffey, Project Manager
Corpus Christi Petrochemical Company
Corpus Christi, Texas 78408
A. S. Athavaley, Senior Process Engineer
R. J. Funk, Project Manager
R. G. Sweet, Senior Engineer
Subsurface Disposal Corporation
Bellaire, Texas 77401
INTRODUCTION
Corpus Christi Petrochemical Company (CCPC) has constructed an olefins plant at
Corpus Christi, Texas, which can crack a variety of feedstocks, primarily naphtha, gas od and
kerosine, to produce the spectrum of olefin products. The major products are ethylene and
propylene, but important byproducts include C4 hydrocarbons, benzene, gasoline, fuel od,
etc. [ 1].
The sulfur compounds in the sour crude feedstock used in the process are mainly converted to hydrogen sulfide (H2S) gas during the cracking operation. The off-gas is commonly
referred to as "sour gas." Some mercaptan and oxygenated organic compounds, such as
aldehydes and carbonic acid, are also formed. Owing to the reactions in the cracking process,
considerable amounts of both carbon dioxide and carbon monoxide are formed. These contaminants are removed in the ethylene purification process to maximize ethylene production
[2]. Scrubbing towers are used to remove the sour gas, carbon dioxide, and other undesirable organic compounds. Typically, ethylene, propylene, butadiene, isoprene, aromatic gasoline, etc., are recovered in the cracking process.
Scrubbing is accomplished using a caustic soda solution as the absorbent makup. The
scrubbing agent is continuously recirculated through the tower and a reject stream, high in
sulfides and carbonates, is withdrawn. Before the spent caustic stream is treated, polymer
and/or oil contaminant concentrations are minimized. The spent caustic is treated with the
aromatic gasoline recovered in the cracking process. The gasoline-washed stream is passed
through a separator to remove most of the free od. Once treated, the spent caustic represents
the wastewater stream for disposal.
The caustic concentration can range from 2 to 5%. The wastewater pH is expected to
range consistently above 13. The sulfide content, as S2', may range from 500 to 35,000
mg/1. It is estimated that about 50 mdlion gallons of wastewater wdl have to be disposed of
annually when the plant is in fud production. This represents a design average flow rate of
about 100 gpm with minima and maxima of 40 and 200 gpm, respectively.
This wastewater cannot be discharged to any watercourse because it is both toxic and
refractory [3]. It cannot be treated economicady for surface disposal, nor does the best
avadable technology produce an acceptable effluent [4]. For example, if the wastewater is
neutralized with acid, II; S and sulfur wdl be generated if the pH is not carefudy monitored
and controlled. Even with close in-plant control, it is possible to release H2 when the waste
stream pH drops below 8 on ddution with surface or rainwater. Further, the acid cost for
neutralization wdl range from $30 to $60 per 1000 gaUons treated based on using hydrochloric acid. Based on the disposal alternatives available, it was determined that the most
practical method for the ultimate disposal of the wastewater was deep wed injection.
This paper presents some of the guidelines which were used to design a disposal facdity
for this waste. The facility design factors were developed from studies of the wastewater
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