ARNOLD, K. (1999). Design of Gas-Handling Systems and Facilities (2nd ed.) Episode 1 Part 5 pps

86 Design of GAS-HANDLING Systems and Facilities

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Generally, the following design criteria should be provided to the man￾ufacturers or vendors for sizing an exhaust heat recovery unit.

1. Total heat duty required to heat the fluid

2. Properties of the fluid to be heated

3. The outlet temperature of the heated fluid

4. Operational relationships between heat sources and users (e.g.,

which users continue to operate when sources shut down?)

5. Exhaust gas flow rates at anticipated ambient and at various loads

from maximum to minimum

6. Exhaust gas temperature at anticipated ambient and at various loads

7. Maximum exhaust back pressure

8. Ambient temperature range

The design of heaters and waste heat recovery units is beyond the

scope of this book. Sizing and design are best left to manufacturers,

However, the concepts discussed in this chapter and in Chapter 2 can be

used to verify the manufacturer's proposals.

HEAT EXCHANGER EXAMPLE PROBLEM

Design a seawater cooler to cool the total stream from the example

field in its later stages of life from a flowing temperature of 175°F to a

temperature of 100°F to allow further treating.

Given:

Inlet 100 MMscfd at 0.67 SG (from Table 2-10)

6,000 bopd at 0.77 SG

15 bbl water/MMscf

T, = 175°F

P, = 1,000 psig

Water vapor in gas = 60 Ib/MMscf (See Chapter 4.)

Outlet T2=100°F

P2 = 990 psig

Water vapor in gas = 28 Ib/MMscf (See Chapter 4.)

Seawater T3 = 75°F

Limit temperature rise to 10°F

Use 1-in. OD 10 BWG Tubes on iM-in. Pitch

Heat Exchangers 87

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1. Calculate water flow rate in outlet and water vapor condensed.

2. Calculate heat duty.

3. Determine seawater circulation rate.

4. Pick a type of exchanger and number of tubes required.

Solution:

1. Calculate free water and water vapor flow rates.

Water flow rate in inlet:

Free water = (100 MMscfd)(15 bbl/MMscfd) = 1,500 bwpd

Water flow rate in outlet:

Free water = 1,500 bwpd

Water vapor condensed:

Water flow rate in outlet:

2. Calculate heat duty

a. Gas duty

T, = 635°R

T2 = 560°R

Tav=597.5°R

Pc = 680 psia (Table 2-10)

PR = P/PC=1.47

Tr = 375°R (Table 2-10)

TR = Tav/Tc = 1.59

qg = 41.7(AT)CgQg

Cg = 2.64 [29 x S x C -f ACpj

C - 0.528 Btu/lb°F (Figure 2-14)