Carbon Management
In the Texaco process, soot is extracted from the carbon-water mixture with naphtha and recycled with the feedstock to the reactor where it is gasified to extinction. The black water from the quench and the scrubbing section is cooled and contacted with the naphtha in the decanter. In this vessel the naphtha extracts the soot from the water leaving much (but not all) of the ash present in the water phase (gray water). The soot-naphtha mixture is drawn off the top of the decanter and mixed with fresh feed oil. The naphtha is recovered in a distillation tower and recycled to the decanter, leaving the soot-oil mixture as a bottoms product for feeding to the gasifier. Traces of naphtha remain in the tower bottoms and are gasified as well. This naphtha slip has to be made up with fresh naphtha to the system.
The gray water is degassed to recover naphtha and recycled for use in the quench and scrubbing sections. When operating in quench mode the overall water balance is negative because of the large amount carried out with the syngas. Nonetheless, a bleed stream of gray water is bled from the circuit to remove ash. This is necessary to limit the buildup of ash in the circuit. This is by no means trivial, and a soot-oil gasifier feed metals content of about ten times that of the fresh feedstock has been reported. A device was developed that reduced this buildup factor to about 2.5 (Czytko, Gaupp, and Muller 1983).
When operating in the syngas cooler mode there is little water in the raw syngas, so that the bleed stream is necessary in any case to maintain the water balance.
Equipment Performance
The equipment for the process has proved reliable in service, and in a study on operation and maintenance aspects of the process, the data in Table 5-10 have been published.
Process Performance
Typical process performance for different feedstocks is shown in Table 5-11.
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Table 5-10 Maintenance Intervals for Texaco Oil Gasifier |
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|
Component |
Frequency |
Time required for intervention |
|
Burner |
every six months |
6-10 hrs |
|
Quench |
every two years |
156-180 hrs |
|
Refractory |
every three years |
680-760 hrs |
|
Source: Bresson and Curcio 1997 |
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Table 5-11 Performance Data for the Texaco Oil Gasification Process |
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|
Feedstock Type |
Natural Gas |
Naphtha |
Heavy Fuel Oil |
Tar (from Bituminous Coal) |
|
Feedstock composition |
||||
|
C, wt% |
73.41 |
83.8 |
87.2 |
88.1 |
|
H, wt% |
22.8 |
16.2 |
9.9 |
5.7 |
|
O, wt% |
0.8 |
0.8 |
4.4 |
|
|
N, wt% |
3.0 |
0.7 |
0.9 |
|
|
S, wt% |
1.4 |
0.8 |
||
|
Ash, wt% |
0.1 |
|||
|
Raw gas composition |
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|
Product gas (25 bar, quench) |
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|
Carbon Dioxide, mol% |
2.6 |
2.7 |
5.7 |
5.7 |
|
Carbon Monoxide, mol% |
35.0 |
45.3 |
47.4 |
54.3 |
|
Hydrogen, mol% |
61.1 |
51.2 |
45.8 |
38.9 |
|
Methane, mol% |
0.3 |
0.7 |
0.5 |
0.1 |
|
Nitrogen + Argon, mol% |
1.0 |
0.1 |
0.3 |
0.8 |
|
Hydrogen Sulfide, mol% |
0.3 |
0.2 |
||
|
Soot, kg /1000 Nm2 |
1.8 |
10 |
6.1 |
|
|
Consumption figures per |
||||
|
1000 Nm3 CO+H2 |
||||
|
Feedstock, kg |
262 |
297 |
323 |
356 |
|
Oxygen, Nm3 |
248 |
239 |
240 |
243 |
|
Steam, kg |
74 |
148 |
186 |
|
|
With permission: ChevronTexaco |
