Бурение грунтовых зондов, установка энергетических колодцев

Typical specifications for carbon monoxide and oxo-synthesis gas are:

Design Considerations

The example will show combined production of 5000 Nm3/h pure carbon monoxide and 5000Nm3/h oxo-synthesis gas, based on natural gas feed. For a plant of this size it is assumed that oxygen is available from a pipeline or a multicustomer gas supply facility.

• There are three principle processes for the manufacture of synthesis gas from natural gas, steam reforming, catalytic autothermal reforming, and partial oxidation. The hydrogenicarbon monoxide ratio of the syngas is an important characteristic distin­guishing between these three processes. Unless there is the possibility of importing C02, the typical range for the three processes with and without C02 recycle is:

Thus the desired ratio of hydrogen and carbon monoxide in the product streams is an important factor in process selection. Note, however, that with partial oxidation, the C02 produced is small and so also the effect of C02 recycle. For this reason, C02 recycle is seldom applied with partial oxidation units.

The other determining issue is primarily economic, namely, the availability of oxygen for both autothermal reforming and partial oxidation. For small plants it is seldom economic to build a dedicated air-separation plant, so where no pipeline oxygen is available or synergies with a gas supplier cannot be realized, steam reforming would be applied, despite the potential hydrogen surplus that can only be used as fuel.

For both oxo-synthesis and pure CO production, all processes supply excess hydrogen so partial oxidation, which produces the lowest H2/CO ratio, is often selected if oxygen is available.

• Looking at the flowsheet in Figure 7-7, one observes that no desulfurization step has been expressly included. The decision regarding what to do about desulfurization will

depend heavily on the amount of sulfur in the gas. One frequently applied possibility is to include a zinc-oxide bed in the natural gas preheat train. However, one needs to pay careful attention to the matter of metal dusting corrosion, particularly at the hot gas inlet of a syngas cooler. The alternative is to place the zinc-oxide bed in the syngas line, upstream of the amine wash, allowing the sulfur to act as a corrosion inhibitor (see Section 6.11). An additional advantage of this choice is that sulfur also inhibits the methanation reaction. Spontaneous methanation at the temperatures pre­vailing is a rare occurrence, but in the presence of catalytic impurities in the gas it can take place. A third possibility, if the sulfur level in the natural gas is sufficiently low, is to remove it with the C02 in the amine wash. The latter must, however, be designed to remove COS as well as H2S, so as to meet the oxo-gas specification, and the sulfur content in the C02 must be within environmentally permitted levels. For the purposes of our example this matter is not included in the mass balance, Table 7-5.

Example

Natural gas is fed to the partial oxidation reactor where it is reacted with oxygen and without any steam moderator to produce a raw synthesis gas. The raw gas is desul­furized with zinc oxide at the outlet of the partial oxidation unit after cooling in a syngas cooler. The raw gas is washed with MDEA to achieve a residual C02 content of lOppmv, which meets the oxo-syngas specification and the requirements of the cold box for the cryogenic separation. In the membrane unit, sufficient hydrogen is extracted from the clean gas as permeate to leave the H2/CO ratio of the non — permeate at 1:1 as required by the oxo-synthesis process.

In the cold box of the cryogenic separation, a 98.5 mol% CO product is obtained, which must be compressed to feed the downstream CO consuming units. Both membrane and cryogenic separation produce a raw hydrogen, which is purified in a PSA unit so that it can be used in the hydrogenation stage of the oxo process or for other purposes. Tail gases from the cryogenic unit and the PSA are available for use as a low-pressure fuel gas.

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