Gas Dehydration Packages

Gas Dehydration Packages

introduction

The removal of water from gas to overcome the risk of hydrate formation to meet the dew point specification is most frequent carried out using a glycol dehydration unit.

THE PROCESS

Wet gas to be dehydrated enters the glycol contactor as shown in the cutaway illustration and is brought into close contact with the glycol by means of bubble cap trays. Bubble cap trays have become the standards as this type of trays hold it s liquid seal both at the low liquid loadings inherent in a glycol unit and under turn down conditions as regards gas flow rate. (Low liquid loadings are a characteristic of the glycol dehydration process since the glycol circulation is a foundation of the water content of the gas being dehydrated rather than the total gas stream. The number of trays used in the glycol contactor as well as the glycol loading and glycol concentration are determined according to the degree of dehydration required. The glycol loading and concentration are established the duty for the glycol regenerator is established

The bubble cap tray used in PARCTEC’s Glycol Dehydration unit employs a bubble cap specifically designed for the purpose and its performance characteristics such as tray efficiency are well proven so that dehydration performance can be confidently predicted and guaranteed.

A glycol regenerator can be used in conjunction with a glycol contactor when the glycol circulation rate and concentration are determined by the glycol contactor design or in conjunction with dehydrate inhibition units when the duty is set by th hydrate inhibition requirements In the case where a glycol contactor is used, tri-ethylene glycol is the most suitable type of glycol, where as for dehydrate inhibition schemes mono-ethylene glycol is more suitable. Tri-ethylene glycol is normally regenerated to greater than 99% concentration for return to the glycol contactor whereas mono-ethylene glycol is generally regenerated to a concentration with in 60-80% level.

The function of the various parts of a global regenerator is as follows:-

This provides the heat necessary to distill the water out of the glycol. It can be heated by any of the following means

1. Direct fired(illustrated)
2. Electricity heated
3. Hot Oil heated

Modulationg control is employed for each type of heating to maintain a steady distillation Whatever type of heating is employed, HupSeng design ensures that the heat flux is limited to avoid thermal degradation of the

STILL COLUMN

Here the glycol/water distillation takes place. A fraction of the steam is condensed to provide reflux, a packed column is generally used for this duty as the vapour-liquid loading is fairly constant.

FLASH DRUM

When the glycol for regeneration contains appreciable dissolved gas, or liquid hydrocarbons, a flash drum is recommended to separate these out to avoid foaming problems in the re-boiler.

GLYCOL HEAT EXCAHNGER

Recovering heat reduces the heat load on the re-boiler reducing utility costs. The heat exchange scheme is optimized on every application to obtain the maximum heat recovery.

The type of heat exchanger can be varied according to preference

1. Coil type(illustrated)
2. Shell and tube type
3. Tube in tube type
4. Plate type

The plate type exchanger is favored for offshore applications due to its compliances and light weight

GLYCOL FILTER

This removes particulate matter which cause fouling of heat exchangers and adversely affects overall performance

CARBON FILTER

Build up of dissolved contaminants can lead to problems such as glycol foaming and deterioration of overall performance. Removal of these contaminants (by absorption on active carbon) generally gives better results than the use of additives such as anti-foams

GLYCOL PUMPS

These re-circulate the glycol to glycol contactor. Normally two pumps are employed, one acting as a standby spare. Glycol, gas or electrically driven pumps are options available. For larger flows the electrically driven pump is generally the best option.

STRIPPING COLUMN

By stripping out the water remaining in the glycol after distillation, a much higher glycol concentration can be achieved. This higher concentration of glycol can be used to give a higher dehydration performance, or can be used to allow a reduction in the number of trays used in the contactor for a reducing in glycol circulation

Of particular importance to the offshore operator is that the use of higher concentration glycol can reduce the size of dehydration unit saving valuable platform space.

GLYCOL COOLER

The hot glycol from the regenerator needs to be cooled to near the operating temperature of the glycol contactor. This can be achieved through several alternative means namely:-

1. Gas / glycol heat exchanger (illustrated with contactor)
2. Air cooled exchanger
3. Cooling water exchanger

The gas / glycol exchanger cannot overcool and so does not need any temperature control whereas air cooled and water cooled units need temperature control to correct for changes in coolant temperature.

KEY DESIGN FEATURES 1. Proven process
2. Minimum gap pressure drop
3. Most economical dehydration process for majority of applications to natural gas drying
4. Basic process flexible and can be adapted to meet individual requirements
5. Continuous process giving constant product specification
6. Easy to operate
CONSTRUCTION

All units can be manufactured to comply with recognized international codes and standards. Skid mounted units designed by our engineers significantly simplify transportation and installation on site, either onshore or offshore.

In all cases instruments, control valves and hook-up of all electrical and pipe work can be included as part of the skid mounted package.

PARCTEC’s Gas dehydration equipment complements an extensive range of process equipment, which includes separation, filters and coalesers, waste heat recovery, Fired heaters, PSA nitrogen generation.