METHANOL INJECTION CALCULATION
INITIAL DATA
Gas Flow Rate Q 12.2 MMSCFD
Gas Pressure P 830 PSI
Gas Specific Gravity g 0.68 -
Initial Gas Temperature ti 104 F
Final Gas Temperature to 35.6 F
Hydrate Formation temperature th 62 F (Values to be taken from GRAPH 1 using pre
Water Content @ ti and P
Water Content @ to and P
-
-
1.75
0
lb/MMSCF
lb/MMSCF
} (Values to be taken from GRAPH 2 SHEET 2
Water removed from gas WG 1.75 lb/MMSCF
Methanol (inhibitor) density @ 60 F and 1 atm - 6.6385 ppg
Methanol (inhibitor) concentration Win 99 %
Methanol (inhibitor) molecular wt MWinh 32 -
Hammerschmidt constant for methanol ( inhibitor) KH 2335 -
Depression of Hydrate formation temperature th 26.4 F
Vapor-phase methanol losses f (P,t) 1.1 - (Values to be taken from GRAPH 3 using pre
METHANOL INJECTION RATE CALCULATION
1. Concentration of methanol (inhibitor) required in liquid phase using Hammerschmidt equation.
th x MWinh x 100
W =
th x MWinh + KH
W = 26.57 %
2. Methanol usage in liquid phase, if methanol enters pure, Win = 100% and is diluted down to Hammerschmidt minimum
WG x MWinh x th
I =
KH
I = 0.633 lb MeOH/MMSCF
Methanol usage in Liquid phase (MeOHw) = 0.633 lb MeOH/MMSCF
3. Methanol usage in gas phase
LBm of vapor MeOH/MMSCF
Vapor-phase methanol losses { f (P,t) } = =
WT % of MeOH in water phase
Methanol usage in Gas phase (MeOHg) = 29.2244795 lb MeOH/MMSCF
4. Total methanol required
Total Methanol = MeOHw + MeOHg
Total methanol = 29.858 lb MeOH/MMSCF
Methanol required = 364.26 lb MeOH/day
Methanol required = 54.87 gal MeOH/day
ULATION
be taken from GRAPH 1 using pressure and specific gravity value from SHEET 1)
be taken from GRAPH 2 SHEET 2 when gas is not undergoing through dehydration process )
be taken from GRAPH 3 using pressure and final gas temperature value from SHEET 3)
1.1
METHANOL REQUIRED = 54.87 gal MeOH/day
METHANOL REQUIRED = 8.65 Liters/Hour
( 1 US Gallon = 3.785 Liters)
HYDRATE FORMATION TEMPERATURE CALCULATION
Gas Pressure PSI 830
Gas Specific Gravity - 0.68
From chart
F 62
Hydrate Formation Temperature
C 16.67
BACK TO MAIN
WATER C0NTENT OF HYDROCARBON GASES
Gas Pressure PSI
Gas Temperature F
From Chart
Water Content of the Gas LB of H20/MMSCF
Note: For systems where gas is not undergoing through dehydration process
BACK TO MAIN
VAPOR PHASE METHANOL LOSSES
Gas Pressure PSI 830
Final Gas Temperature F 35.6
From Chart
LBm of vapor MeOH/MMSCF 1.1
WT % of MeOH in water phase
BACK TO MAIN
METHANOL INJECTION THEORY
Point 1: For methanol injection:
a. Density slightly less than water and must be dispersed and distributed thoroughly within the process media for maximum contact time.
b. Requires continuous direct injection distributed via an atomizer.
Point 2: Inlet Moisture Considerations
Inlet gas moisture (water) content control is required to maintain continuous operation of the gas conditioning process. It is crucial that on
dehydrated inlet gas be fed to the skid inlet to avoid ice and hydrate problems.
Dew Point Control recommends the following precautions to help prevent hydrate and ice formation:
1. When operating at cold separator temperatures of 35 degrees or higher:
Dehydrated gas fed to the DPC unit should have no more than 7 LB/MMSCF of water content.
Methanol injection is not normally needed with a properly operating glycol unit, although it is recommended that methanol be injected for
to keep the system clean.
2. When operating at cold separator temperatures below 35 degrees:
Dehydrated gas fed to the DPC unit should have no more than 3 LB/MMSCF water content, requiring, in most cases, stripping gas on the re-
an eight tray contactor, and a reboiler temperature of no less than 385 degrees. Methanol injection is recommended to keep unit clear of hy
operating below 35 degrees. When the unit chills the gas to the vicinity of hydrate formation or ice formation temperature, methanol must
DPC provided on-skid pump. When using DPCs high efficiency methanol injection system, methanol flow should be set at 2.5 pounds of me
of inlet water by setting the strokes per minute of the injection pump. (1.2 gallons of methanol per MMSCF of 3# gas)
Because of the potential for a freeze blockage in the unit, it is strongly recommended that a pressure controlled unit bypass be installed acr
piping to permit continuous gas delivery to the pipeline until skid operation can be restored to normal. If the pipeline will not permit offspe
thawing, or other system troubleshooting, then provision should be made to safely dispose of the off-spec gas during these periods, such as
located safely at the edge of the facility and away from any exposure to neighboring personnel, residents, houses, businesses, etc.
a for maximum contact time.
g process. It is crucial that only a properly
hat methanol be injected for one shift per week
ases, stripping gas on the re-concentrator reboiler,
nded to keep unit clear of hydrates and ice when
emperature, methanol must be injected using the
ld be set at 2.5 pounds of methanol per pound
3# gas)
d unit bypass be installed across the inlet and outlet
ipeline will not permit offspec gas to flow for startu
during these periods, such as a flare or vent stack
es, businesses, etc.
BACK TO MAIN
