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Application of Block Heat Exchangers in Natural Gas Dehydration

Fully welded plate heat exchanger – predestined for oil and gas

Introduction

Dehydration of natural gas is a substantial issue to guarantee transport safety. Highly flammable methane is one of the main components of natural gas which reacts together with hydrogen and forms methane hydrate. This reaction can cause massive pressure drops in the feeding pipelines and subsequently may initiate defects in pipes, valves and other fittings.

Dehydration process

The so called GDU process of gas dehydration (GDU - Gas Dehydration Unit) removes water from the natural gas and this avoids the formation of solid methane hydrate during the transport. The degree of drying of the natural gas is determined by the dew point which should be lower than -8°C to guarantee for a safe transport. Furthermore, the process of drying secures a constant ca-lorific value of the natural gas when fed into the grid.

In the dehydration process, often strongly hygroscopic tri-ethylene glycol (TEG) is used which extracts the water from the natural gas in a counter current procedure. In Fig. 1 the schematic process is shown primarily basing on an absorber (1), a glycol heat exchanger (6), a flash drum for pressure reduction (2) as well as a FunkeBloc heat exchanger (3) and a stripper column (4).

Gas dehydration with FunkeBloc

In a first step, in the absorber (1) the wet natural gas gets into contact with the glycol in a counter current process. The gas flows in from the bottom and by using of the hygroscopic effect of the tri-ethylene glycol flowing in from the top, the water is removed. The largest possible contact area between the two media should be achieved. Now the dried gas (dew point < - 8°C) runs through a gas glycol heat exchanger to cool down the glycol (6) and it is then ready for further treatment.

To achieve a continuous process of natural gas dehydration, the glycol-water mixture has to be dehydrated and cleaned in the further process. For this regeneration, the pressure of the medium is reduced to the required regeneration pressure in a flash drum (2). Also hydrocarbons, picked up during the dehydration process, are eliminated.

Subsequently, the heat energy bound to the cleaned glycol (Lean Glycol/Lean TEG) is used to heat up the charged glycol (Rich Glycol/Rich TEG) in a heat exchanger. This heat recovery is able to reduce decisively the amount of required primary energy. Here for example a highly efficient, fully welded plate heat exchanger type FunkeBloc with high surface density can be applied.

The pre-heated charged glycol is now fed into a stripper column (4) in which humidity and fou-ling substances are removed from the glycol again. After this, the cleaned glycol flows through a reboiler and back to the heat exchanger while cooling down. By means of a glycol pump (5) the pressure of the medium is increased again to the required absorption pressure, after giving off the remaining heat in an additional gasketed heat exchanger (e.g. Funke type FP) or directly in a gas-glycol heat exchanger (6). The cleaned and dehydrated tri-ethylene glycol is now again available for the dehydration process.

Table 1 gives an overview of the typical process parameter for heat transfer in the unit (3):

  Design Parameter Operation Parameter
  Pressure [bar] Temperature [°C] Pressure [bar] Temperature [°C]
Rich TEG 0-10 up to 230 4.5 72 to 171
Lean TEF 0-10 up to 230 1.0 195 to 85

Process parameter inside FunkeBloc heat exchanger

Fully welded plate heat exchanger – predestined for oil and gas

The FunkeBloc series is mainly used in chemical and petrochemical industries as well as in re-fineries and with oil and gas treatment. The typical applications, besides the heat recovery as shown in the example, include also the classical process heating and cooling as well as conden-sation and vaporisation. According to the design, the high-quality heat exchangers offer operation temperatures from – 50 to +400 °C and pressures from -1 to 40 bar.

To protect the heat exchanger from corrosion, all media contacted components are made from stainless steel or other corrosion resistant materials.

The unique feature of the heat exchanger is above all the highly efficient design with high surface density.

In comparison to shell-and-tube heat exchangers, the heat transfer area can be significantly reduced resulting in low investment and maintenance costs. The compact Bloc design secures opening for maintenance and inspection in a minimum of space.

The latest software, verified by empiric results for the manufacturer’s own test laboratory*, is used for design and dimensioning of the heat exchanger type described here. However, complex cases can also be calculated using the HTRI software.

The mechanical design considers all applicable codes as EN13445, ASME VIII, Div 1, API662 or NACE MR0175 / MR0103 to fulfil highest requirements.

Insight-Modell of FunkeBloc FPB006

Insight-Model of FunkeBloc FPB006: maintenance and cleaning friendly concept, the unit can be inspected internally completely without disassembling.

* also see article „Leistungsparameter von Wärmetauschern unkompliziert ermitteln und bewerten“ , Chapter 1 „Simulation/Auslegung“

Author:

Martin Dierich

Graduate Engineer

Martin Dierich

Manager WPHE
Sales & Thermal Design

FUNKE Wärmeaustauscher Apparatebau GmbH

Zur Dessel 1
31028 Gronau/Leine
Germany


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