Feed and Product Properties Natural Gas Feed

COMPONENT MOL%

COMPOSITION

CARBON DIOXIDE 2.20

NITROGEN 0.65

METHANE 89.10

ETHANE 6.31

PROPANE 0.34

ISOBUTANE 0.30

iV-BUTANE 0.60

ISOPENTANE 0.20

N-PENTANE 0.20

HYDROGEN SULFIDE, ppmv 400

MERCAPTANS, ppmv 600

TOTAL 100.00

TEMPERATURE, °F 110

PRESSURE, psig 480

Table 5-8 Product Hydrogen

COMPONENT

HYDROGEN, MOL% 97

METHANE & NITROGEN REMAINDER

with Benfield solution flowing from the top of the column. C02 is removed from the gas stream by a solution of potassium carbonate, promoted by DEA and containing a vanadate corrosion inhibitor (approximately 25.7% potassium carbonate and 4.76% diethanol amine).

Part of the potassium carbonate is converted to bicarbonate on each pass. Since the cooler solution has a lower carbon dioxide vapor pressure, the top part of the C02 absorber is provided with a cooled stream of solution. The remainder of the solution enters the absorber lower down with no cooling.

The hot, rich solution flows to the top of C02 stripper C-105 (Benfield solution regenerator), where it is regenerated by contact with steam rising

CARBONATE R EGENERATOR C-105

REGENERATOR REFLUX DRUM V-106

CARBONATE ABSORBER C- 104

CARBONATE ACID GAS TO

REGENERATOR ATMOSPHERE

OVERHEAD CONDENSER E-ior

CARBONATE R EGENERATOR C-105

REGENERATOR REFLUX DRUM V-106

CARBONATE ABSORBER C- 104

H2s Absorber Column

Figure 5-2. Hydrogen plant C02 removal and methanation. LP = low pressure.

from solution reboilers attached to the base of the column. A large proportion of the reboiler heat is provided from the gas stream, and the remainder is obtained from low-pressure steam (65 psia) condensed in the steam reboiler.

C02 and steam leaving the top of the column is cooled sufficiently to maintain the system water balance and vented to atmosphere. In locations where visible plume is not permitted, it is cooled 20-30°F above ambient temperature before venting it to atmosphere. Surplus condensate in this situation is degassed and sent to an off-site area for treatment.

The solution from the base of the C02 stripper is pumped to a C02 absorber. A part of the solution is cooled and sent to the top of the column, while the remainder enters the bottom half of the column with no cooling. Both columns are packed with metal pall rings packing.

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