Glycol Degradation

GLYCOL RECLAIMER


The following article was selected for presentation at  K. Dave Diba, M. Guglielminetti, S.Schiavo

ABSTRACT
All glycols used for dehydration by absorption in counter current Tri-ethyleneglycol (TEG), and Mono-ethylene glycol (MEG) used for glycol injection for hydrate prevention will require reclaiming. The
intervals at which reclaiming is required will vary from a month or two for very
foul solutions to a year or more for those that are properly conditioned in the course
of operation.
It should be remembered that glycol solutions are small in quantity compared to the multi-millions cubic meters of gas and condensate that they contact.
Contaminants such as salts, lube oil, hydrocarbon condensate, crude oil and corrosion products are present in abundance in liquid phase and in minute “trace” amount in the gas; and they continually plague operators in their glycol systems, and the symptoms of these problems are fouled equipment, foaming in the system resulting in expensive glycol losses, and insufficient process capability.
Shutting a plant down to thoroughly clean and repair all the equipment is a periodic necessity and very expensive.
MEG catches most contaminants and they accumulate in the plant’s glycol inventory until they create severe operational problems. Most operators drain the contaminated glycol charge and discard it, replacing it with a charge of new glycol.
This begins a new cycle that ends in the same way month(s) later. Other plants loose so much contaminated
glycol in “normal operations” that replacing the losses with new glycol keeps the contamination at a tolerable level due to continuous addition of “makeup” glycol.


INTRODUCTION
It is the purpose of this paper to review the contaminants, the basic technology available, and the facilities available for reclaiming glycols.
Contaminants
Principal among these are:
1. Organic acids
2. Inorganic acids
3. Iron carbonates and iron sulfides, products of corrosion caused by CO2 and H2S in the feed gas.
4. Decomposition products from glycol degradation, and heat stable salts.
5. Coke formed by thermal decomposition of heavy hydrocarbons in glycol emulsion.
6. Crude oil, condensate and compressor lube oil in glycol emulsion.
7. Aromatic hydrocarbons that dissolve in glycols.
8. Salts, and total solids from entrained formation water and condensate.
Special attention must be given to the chemical and physical properties of these contaminants. All reclamation
technology must be based on differences in these properties in order to achieve good separation from glycol
that carries them in solution or suspension in the reclaimer feed.
RECLAIMER PRINCIPLES
Two basic principles have been applied to glycol reclaiming.
The first is electro-dialysis. Since the glycols are nonpolar, the feed must be diluted with water to at least 30
WT% or more water to enable the process to operate and transfer the chloride ion through the membrane in
exchange for hydroxyl ion. The product, chloride free glycol, must be distilled to remove the excess water. In
this application careful cleaning of feed is absolutely essential if the membranes are to remain operable. The
energy requirement, cleaning and maintenance cost for this method is very high.
The second is vacuum distillation where heat and vacuum are used to boil off all glycol and lighter components, leaving as residue the salts, other heavy high boiling point tars and degradation materials. This paper will be devoted to requirement for complete glycol reclaimer which employs vacuum distillation.

This process comprises three essential operations arranged in the following sequence prior to reclaimer.
1- Removal of all solids. This step is accomplished through a properly designed cartridge filter(s) in the glycol
regeneration skid.
2- Breaking of oil in glycol emulsions and removal of most of aliphatic condensate. This step is accomplished
through a properly designed horizontal three phase separator (AKA flash tank) in the glycol regeneration
skid.
3- Distilling of the light ends, water and organic acids. This step is accomplished through a properly designed
glycol reboiler, still column, and reflux condenser in the glycol regeneration skid.
The glycol reclamation is carried out on batch or continuous basis; this depends on the amount of impurities added to the glycols during the plant operation. The major contributor of glycol fouling is soluble salts carried into the glycol system. Therefore, gas dehydration by TEG requires less frequent reclamation since very little soluble salt is carried into the TEG dehydration, the presence of acid gases and TEG degradation will determine how often the total TEG solution should be reclaimed (batch); or if the fouling of TEG is very severe due to any or combination of above sources of contaminants, then a slip stream (continuous) of TEG to be reclaimed.
Note: Generally the continuous TEG reclamation is carried out only in those gas dehydration applications with high acid gas content.
In MEG process for hydrate prevention (wet gas evacuation) the presence of formation water salts, corrosion inhibitors, surfactants, heavy hydrocarbon liquid, and if sour gas(ses) are more commonly present; their accumulation in the MEG solution will increase very rapidly; therefore, this necessitates a slip stream (continuous) MEG reclamation.
This reclamation rate varies between 3% lean MEG circulation for moderate salts accumulation up to 20% of
lean MEG circulation for heavy salts accumulation.


CONCLUSION
The glycol reclaimers have been used for numerous severe applications with great results in saving for glycol losses, lower maintenance, and meeting process requirement continuously. It has been shown that with on-stream reclaimer systems the glycol systems have not been shut down for cleaning or repairs for several years. These units have been designed and built as mobile trailer mounted self contained systems for transportation with small truck to different locations (Please see attached photograph); or as a dedicated skid mounted plant in one location. The same reclaimer can handle both MEG and TEG (separately) on batch or continuous mode.
Few example cases are described below:
1- Coke oven gas dehydration (Indiana, USA) contained high concentration of naphthalene, and high molecular weight hydrocarbon, causing glycol to become very viscous and difficult to flow through the dehydration system and gas dehydration had to be stopped every three weeks for cleaning and changing the glycol. Since the installation of the reclaimer in 1984 no unscheduled stoppage has occurred.
2- Sour gas dehydration (Texas, USA) contained high H2S and CO2 acid gasses. Since the reclaimer started running continuously the glycol losses and plant equipment cleanup has been reduced below normal
standard.
3- Mobile glycol reclaimers (Pennsylvania, Ohio USA) were used to clean stored contaminated glycol, or used on operating plants. In these mobile units an atmospheric reboiler was “piggy backed” on top of vacuum reboiler for boiling off most of the “Rich” contaminated glycol water and light hydrocarbons prior to entering the vacuum reboiler.

4- Gas dehydration (Offshore Canada) the wet gas
evacuation contained high salt content resulting in
severe salt contamination in the equipment, in one
instance due to some excess water carryover the salt
content shut up to above 95000ppmw in glycol; with
reclaimer operating and the lean glycol feed containing
95000ppmw salt the reclaimed glycol salt content was
below 60ppmw.