TYPICAL CONDITION WHICH EFFECT GLYCOL LOSSES

Typical Condition Which Effect Glycol Losses

• Carryover with outlet gas leaving the contactor.
• Leaks at the pump or pipe fittings.
• High still overhead temperature.
• Contactor column operating at excess gas rates.
• Foaming.
• Rapid changes in the gas rate.

But
Who do we know if our system operating efficiently or not. Well, we take glycol samples in the field have lab test them, in term of the results then you make the necessary adjustments to reach maximum drying efficiency.
Now we can find out by analyzing the glycol, now it can tell us

• Glycol weight percentage
• Water content
• Hydrocarbon content
• Salt contaminant
• Solids contaminant
• The pH of glycol
• Iron content
• Foaming tendencies

Glycol weight Percentage
The glycol weight percentage reefer’s to the amount of glycol in the glycol solution also known as glycol purity.

• Lean glycol should contain about 98.5 to 99.9% glycol.
• Rich glycol content varies about 93 to 96% glycol.

Let’s assume rich glycol sample is in the acceptable range (94.7%) but the lean glycol (97.4%) is outside the acceptable range. This means there may need to be some adjustment made.

Water content

Water content refers to the amount of water in the glycol solution. Low water content in lean glycol is vital to good dehydration. The water content in lean glycol shouldn’t exceed 1.5%. If the water content exceed 1.5%, then re-boiler temperature is too low or heater not working properly. The water content in rich glycol shouldn’t be more than 5 to 6 %.

Water Content Spread

Water content spread referred to the difference in water content between lean and rich glycol, a spread which is too narrow 0.5 to 2% usually means the glycol circulation rate is too high, the rate should be lower to safe energy minimize glycol losses and approve dehydration, a spread over 4 to 6% is too wide usually means circulation rate is too low and should be increased.

Circulation Rate

To remove 1 pounds of water use three gallons of glycol. (11 liters /.45 kilograms)

Hydrocarbon Content

Hydrocarbon content refer to the amount oil paraffin or condensate in the glycol, keep it below 0.1% otherwise problem such as foaming, plugging or foaling will cause glycol loss, import dehydration of the gas. Hydrocarbons get into glycol in two ways.

Hydrocarbons get into glycol by

• Condensing in contactor when glycol is colder than incoming gas.
• Carryover of hydrocarbons contaminants from inlet separator or gas stream. (If unit have no separator)

Salt Content
Salt content refer to the amount of salt or chloride in the glycol, it should be capped below 0.01% by wt. or 100 ppm. Problems occur when the salt content reaches almost 0.1% by wt. or 1000 ppm.

·         Salt build-up

These problems include a build-up of salt on the re-boiler fire tube, resulting in decrease heat transfer efficiency.

·         Corrosion

 Which will eventually decay the fire tube.

·         Hotspot

Hotspot on the fire tube resulting in thermal decomposition of glycol and holes in the fire tube.

Salt usually travels in the gas stream in a fine mist, now if the gas stream contains excessive salt, a filter type separator can be used to remove salt from the gas up-stream of the dehydration unit.

Solid Content
Solid contents referred to the amount of suspended solids in the glycol, suspended solids should be kept below 0.01% by wt. using filtration.

High solid content cause

·         Increased pump wear from abrasion.

·         Accelerated corrosion and erosion.

·         Increased fouling of fire tube.

·         Increase glycol loss due to foaming.

·         Increased plugging problems.

pH Scale
pH scale referred to the corrosiveness of glycol, pH is a term use to express acidity or alkalinity. It is based on a 0 to 14 scale.

Acidic	Neutral	Alkaline
0 to 6.9	7	7.1 to 14

A pH about 7.3 is consider as save operating level, as glycol pH decreases the equipment corrosion rate increases rapidly and troublesome corrosive compound result. Raising the pH above 8 to 8.5 is not desirable because of more alkaline glycol solution tills to foam and emulsify easily.
Check the pH of glycol periodically and kept on the alkaline side by neutralizing the acid compound with alkaline chemicals.

Iron Content

Iron content referred to the amount of corrosion products in the system. Rust is most common. Corrosion products either come in the incoming gas or they are result of corroding glycol system. If the iron content exceed 10 to 15 ppm than corrosion prevention methods should be consider.

Foaming Tendency

Foaming referred to the foaming tendency of glycol caused by contaminates. These contaminants in the glycol inner the system as gas entrainments water and glycol alone will not cause significant foaming. However the combination of water glycol and oil does create excessive foaming.

Main foaming problems

·         Improper gas dehydration

·         Excessive glycol losses when glycol foams out of the contactor.

·         Equipment problems downstream of contactor from glycol carryover.

Anti-Foam Additives

Foaming problems can temporary be corrected by anti-foam additives which cause the foam to break. The cause of the problem should than be identify and corrected.

Improper use of anti-foam

Improper use of anti-foam additives can cause increase foaming problem.

The best preventer measure against foaming is the installation of properly design inlet gas separator and glycol filtration system, good glycol filter maintenance and pH control are also very important.