Page 134 - Petroleum Production Engineering, A Computer-Assisted Approach

Guo, Boyun / Computer Assited Petroleum Production Engg 0750682701_chap10 Final Proof page 129 4.1.2007 8:26pm Compositor Name: SJoearun

SEPARATION SYSTEMS 10/129
q
. Overheating of solution may produce both low and high q s ¼ , (10:7)
boiling decomposition products. C t C g
. The resultant sludge may collect on heating surfaces, where
causing some loss in efficiency, or in severe cases, com-
plete flow stoppage. q ¼ gas capacity of contactor at operating conditions,
. When both oxygen and hydrogen sulfide are present, MMscfd
corrosion may become a problem because of the forma- q s ¼ gas capacity of contactor for standard gas
tion of acid material in glycol solution. (0.7 specific gravity) at standard temperature
. Liquids (e.g., water, light hydrocarbons, or lubrication (100 8F), MMscfd
oils) in inlet gas may require installation of an efficient C t ¼ correction factor for operating temperature
separator ahead of the absorber. Highly mineralized C g ¼ correction factor for gas-specific gravity
water entering the system with inlet gas may, over long
periods, crystallize and fill the reboiler with solid salts. The temperature and gas-specific gravity correction fac-
. Foaming of solution may occur with a resultant carry tors for trayed glycol contactors are given in Tables 10.9
over of liquid. The addition of a small quantity of anti- and 10.10, respectively. The temperature and specific grav-
foam compound usually remedies this problem. ity factors for packed glycol contactors are contained in
. Some leakage around the packing glands of pumps may Tables 10.11 and 10.12, respectively.
be permitted because excessive tightening of packing Once the gas capacity of the contactor for standard
may result in the scouring of rods. This leakage is col- gas at standard temperature is calculated, the required
lected and periodically returned to the system. minimum diameter of a trayed glycol contactor can be
. Highly concentrated glycol solutions tend to become calculated using Fig. 10.10. The required minimum diam-
viscous at low temperatures and, therefore, are hard to eter of a packed glycol contactor can be determined based
on Fig. 10.11.
pump. Glycol lines may solidify completely at low tem-
peratures when the plant is not operating. In cold wea- Table 10.9 Temperature Correction Factors for Trayed
ther, continuous circulation of part of the solution Glycol Contactors
through the heater may be advisable. This practice can
also prevent freezing in water coolers. Operating temperature (8F) Correction factor (C t )
. To start a plant, all absorber trays must be filled with
glycol before good contact of gas and liquid can be 40 1.07
expected. This may also become a problem at low cir- 50 1.06
culation rates because weep holes on trays may drain 60 1.05
solution as rapidly as it is introduced. 70 1.04
. Sudden surges should be avoided in starting and shut- 80 1.02
ting down a plant. Otherwise, large carryover losses of 90 1.01
solution may occur. 100 1.00
110 0.99
10.3.2.3.3 Sizing Glycol Dehydrator Unit Dehydrators 120 0.98
with TEG in trays or packed-column contactors can be sized Source: Used, with permission, from Sivalls, 1977.
from standard models by using the following information:

. Gas flow rate
. Specific gravity of gas Table 10.10 Specific Gravity Correction Factors for
. Operating pressure Trayed Glycol Contactors
. Maximum working pressure of contact
. Gas inlet temperature Gas-specific gravity (air ¼ 1) Correction factor (C g )
. Outlet gas water content required
0.55 1.14
One of the following two design criteria can be employed: 0.60 1.08
0.65 1.04
1. Glycol/water ratio (GWR): A value of 2–6 gal TEG=lb m 0.70 1.00
H 2 O removed is adequate for most glycol dehydration
requirements. Very often 2.5–4.0 gal TEG=lb m H 2 Ois 0.75 0.97
used for field dehydrators. 0.80 0.93
2. Lean TEG concentration from re-concentrator. Most 0.85 0.90
glycol re-concentrators can output 99.0–99.9% lean 0.90 0.88
TEG. A value of 99.5% lean TEG is used in most designs. Source: Used, with permission, from Sivalls, 1977.

Inlet Scrubber. It is essential to have a good inlet scrubber
for efficient operation of a glycol dehydrator unit. Two-phase Table 10.11 Temperature Correction Factors for
1
inlet scrubbers are generally constructed with 7 ⁄ 2 -ft shell Packed Glycol Contactors
heights. The required minimum diameter of a vertical inlet
scrubber can be determined based on the operating pressure Operating temperature (8F) Correction factor (C t )
and required gas capacity using Fig. 10.9, which was prepared
by Guo and Ghalambor (2005) based on Sivalls’s data (1977). 50 0.93
60 0.94
Glycol-Gas Contactor. Glycol contactors are generally con- 70 0.96
1
structed with a standard height of 7 ⁄ 2 ft. The minimum 80 0.97
required diameter of the contactor can be determined 90 0.99
based on the gas capacity of the contactor for standard 100 1.00
gas of 0.7 specific gravity at standard temperature 100 8F. 110 1.01
If the gas is not the standard gas and/or the operating 120 1.02
temperature is different from the standard temperature, a
correction should be first made using the following relation: Source: Used, with permission, from Sivalls, 1977.