A Design presentation on

Natural Gas Processing Plant

Presented by :

Abdulla-Al-mamun

St. ID: 0802021

Dept: Ch.E.

BUET

Objectives

By using Aspen hysis simulation

Ensuring more efficient and profitability design.

Improving plant control, operability.

Eliminating process bottle necks and minimizing process network.

Reducing human error and time requirement.

Definition of the project

Location- Kailashtilla, Sylhet

Capacity-550 MMSCFD

Raw materials-Raw Natural Gas From 3 Producing Gas Wells

DEAmine Solution, TEG.

Utility- Electricity(2 MW Capacity), Natural Gas.

Available Process

Gas Sweetening

Solid Bed Sweetening Process:

Molucular Sieves

Aquasorption Process (Wash Water

Process)

Selexol Process

Chemical Absorption

Process(MEA,DEA,TEA Processes)

The Holmes-Stretford Process

Gas Dehydration

Absorption Process(Methanol,

Glycol Process)

Adsorption Process (Solid

Dessicants, Alumina, Silica Gel,

Molecular Sieves)

Design Basis

Climate Condition-

Ambient Temperature- Max- 35OC

Min-12OC

Design max temp- 40OC

min temp-5OC

Annual Avg. Atmospheric pressure-0.11 MPa

Annual Avg. relative Humidity- 80%

Wind Velocity-52 miles/hr

Rain- Annual Avg. Rainfall- 2850 mm

Process Block Diagram

Hysis Simulation

Comparison Between Raw Natural gas & Product gas

Raw Natural Gas

Components Composition

Methane 0.8634

Ethane 0.0574

Propane 0.0088

i-Butane 0.0007

i-Butane 0.0005

n-Pentane 0.0005

n-Hexane 0.0003

H2O 0.0467

Nitrogen 0.0018

CO2 0.0204

Product Gas

Components Composition

Methane 0.930973

Ethane 0.053632

Propane 0.000658

i-Butane 0.000022

i-Butane 0.000014

n-Pentane 0.000007

n-Hexane 0.000002

H2O 0.000101

Nitrogen 0.002029

CO2 0.012562

List of Equipment

Equipment Name QuantityDesignation in the HYSYS Simulation

Compressor 1 K-100

Heat Exchanger 2 E-100, E-102

Absorber 2 T-100, T-102

Separator 3 V-100, V-101, V-104

Pump 2 P-100, P-101

Storage Tank 1 V-106

Stripper Column 2 V-102, V-103

Stabilizer Column 1 V-105

Shell and tube heat exchanger design parameter (E-100)

Tube side (cold fluid)

Inlet fluid: Glycol to be preheated (67.59o F)

Outlet fluid: Preheated glycol to absorber (770F)

Shell side (Hot fluid)

Inlet fluid: Dry gas (99.880 F)

Outlet fluid: Sales gas (94.860F)

Calculation

Q = Uassume Arequired LMTD

For light - heavy organics

Overall U = 10-40 Btu/hr ft20F

Assume, Uassume = 35 Btu/hr ft20F

Arequired = 3147.4 ft2

Calculated tube no 182

Where,

1 shell pass & 6 tube pass(np).

Fixed tube plate

1.5 in. OD(d0), 16 BWG, 1.785in. square pitch, ID (di) 1.37 in,

Selected shell ID (Ds) is 35 in

Clean overall heat transfer coefficient (Uc) calculation, Uc = 42.3 Btu/hrft20F

Over design calculation:

% of over design = 20.86 % < 30 %

So, design is accepted.

Dirt factor calculation

Dirt factor, Rd = 0.00098

Because for natural gas Rd, allowable=0.001

(Ref: Mechanical Design of Process System (vol-2))

Therefore, Rd is acceptable.

Pressure drop calculation

Tube side calculation

Frictional pressure drop = 2.22 Psi

Return loss = 0.34 Psi

So, total pressure drop in tube side, 2.56 Psi < 8.7 psi which is acceptable.

Shell side calculation

Assumption:

25 % cut segmental baffles

Baffles spacing, B = 0.5 Ds = 17.5 in = 1.46 ft (half of the shell ID is selected)

Pitch, Pt = in. square pitch = 0.15625 ft

Clearance, C = Pt – do = 0.03125 ft

Shell ID, Ds = 35 in = 2.92 ft

So, pressure drop = 9.38 Psi < 14.5 Psi, which is acceptable.

P & ID Diagram

TT

TI

AC P/I

Preheated glycol

Heated glycolTo absorber

Dry gas

Sales gas

Figure: 1 shell pass - 6 tube pass heat exchanger

Overall Economic Analysis

Equipment Cost at Present(2014)- $1.088 million

Total Capital Investment - $ 6.12 million

Total Annual Expenses- $ 13.24 million

Net Profit After Tax(15%)- $ 15.4 million

Pay back period – 3 year 11 month

Salvage value- $ 0.532 million

Depreciation- $0.765 million/year

IRR i% = 24.58 %

ERR i% = 19.67%

Project life – 20 years

The End