Refinery Gas Treating Processes

Abstract

Refinery gas treating removes the so called “acid gases” (hydrogen sulfide and carbon dioxide) from the refinery gas streams. Removal of the acid gases in the refinery streams is required either to purify a gas stream for further use in a process or for environmental reasons. This chapter describes the most common sour gas treating processes. Design techniques are provided for the amine-based approaches along with a design example.

David S. J. Jones: deceased.

Steven A. Treese has retired from Phillips 66.

Appendix Process Design of an Amine Gas Treating Unit

The following is an extract from a design specification and defines the parameters of this example:

• 1. Unit required is a gas treating unit for the removal of H₂S from a hydrotreater recycle gas stream. The feed to the hydrotreater consists of gas oil from straight run source and streams from a thermal cracker and a catalytic cracker. The recycle gas will therefore contain some COS.

• 2. The feed gas shall have the following properties:

  • The mole weight of the gas is 10.5.

  • The H₂S content of feed gas is 4,048 grains/100 scf.

  • The gas rate is 30 MMscf/day

  • The pressure of the gas at the outlet of the contactor is 320 psig.

• 3. Product gas shall have a H₂S content no greater than 0.1 grain/100 scf.

• 4. The amine solvent to be used shall be monoethanolamine:

  • Amine ratio to H₂S shall be 3.0 mole amine to 1.0 mole H₂S.

  • The amine solution shall be 20 % by weight in water.

  • Residual H₂S in the lean amine solution shall be no greater than 0.09 mole per mole of MEA.

  • Protection against degradation of the amine shall be included.

The Contactor Design

Calculating the Amine Solution Circulation Rate

$$ \begin{array}{c}\mathrm{Feed} \mathrm{gas} \mathrm{rate} =30\;\mathrm{MMscf}/\mathrm{day}\\ {} =3, 306.9\;\mathrm{mol}/\mathrm{h}\\ {} =34, 722\;\mathrm{lb}/\mathrm{h}\end{array} $$

$$ \begin{array}{c}{\mathrm{H}}_2\mathrm{S} \mathrm{in} \mathrm{f}\mathrm{eed} =\frac{4, 048\times 0.0022857}{16}=0.578\;\mathrm{lb}/100\;\mathrm{s}\mathrm{c}\mathrm{f}\\ {} =5, 100\;\mathrm{mol}/\mathrm{day}=1.928\;\mathrm{MMscf}/\mathrm{day}\\ {} =212.5\;\mathrm{mol}/\mathrm{h}\end{array} $$

$$ \begin{array}{c}{\mathrm{H}}_2\mathrm{S} \mathrm{in} \mathrm{product} \mathrm{gas} =0.1\;\mathrm{grain}/100\;\mathrm{s}\mathrm{c}\mathrm{f}\\ {} =0.126\;\mathrm{mol}/\mathrm{day}\\ {} =0.00521\;\mathrm{mol}/\mathrm{h}\end{array} $$

$$ \begin{array}{c}{\mathrm{H}}_2\mathrm{S} \mathrm{absorbed} \mathrm{in} \mathrm{amine} =212.5-0.00521\\ {} =212.49\;\mathrm{mol}/\mathrm{h}\end{array} $$

The amine ratio is 3.0 mol amine per mole H₂S.

Moles amine circulating = 637.47 mol/h = 38,949 lb/h (mol wt. MEA = 61.1), or for 20 % wt solution = 194,747 lb/h, made up of 155,798 lb water and 38,949 amine.

• lb/gal MEA = 8.45

• lb/gal water = 8.328

• MEA gals/h = 4,609

• Water gals/h = 18,708

Amine solution circulation rate = 23,317 gals/h (volumes are additive in these solutions).

Calculating the Number of Trays and the Overall Dimensions of the Contactor

The number of theoretical stages required in the contactor will be calculated using the equation

$$ N=\frac{\left(\mathrm{Log}\;1/q\left(A-1\right)\right)}{\left(\mathrm{Log} A\right)}-1 $$

(10)

where:

• N = number of theoretical trays

• q = mole H₂S in lean gas/mole H₂S in feed gas

• A = the absorption factor L/V ∙ K

$$ \begin{array}{c}``q" \mathrm{in} \mathrm{this} \mathrm{case} =\frac{\mathrm{moles} {\mathrm{H}}_2\mathrm{S} \mathrm{in} \mathrm{lean} \mathrm{gas}}{\mathrm{moles} {\mathrm{H}}_2\mathrm{S} \mathrm{in} \mathrm{feed} \mathrm{gas}}\\ {} =\frac{0.00521}{212.5}\\ {} =2.45\times {10}^{-5}\end{array} $$

$$ \begin{array}{c}\mathrm{Total} \mathrm{mol}\mathrm{es} \mathrm{of} \mathrm{acid} \mathrm{gas} \mathrm{absorbed} =212.49\;\mathrm{mol}/\mathrm{h}\\ {}\mathrm{A}\mathrm{cid} \mathrm{gas} \mathrm{residual} \mathrm{in} \mathrm{the} \mathrm{lean} \mathrm{amine} =57.37\;\mathrm{mol}/\mathrm{h}\\ {}\mathrm{Total} \mathrm{acid} \mathrm{gas} \mathrm{in} \mathrm{grains}/\mathrm{h} =\frac{269.87\times 34\times 16}{0.0023}\\ {} =63.83\times {10}^6\mathrm{grains}/\mathrm{h}\\ {}\mathrm{Total} \mathrm{M}\mathrm{E}\mathrm{A} \mathrm{solution} =23, 317\mathrm{gal}/\mathrm{h}\end{array} $$

Then grains acid gas per gal of amine solution = 2,738 grains H₂S/gal MEA.

From Fig. 2a for 20 % MEA solution, the H₂S partial pressure is 0.33 psia.

Using the following equation, the absorption factor A is calculated:

$$ A=\frac{a\left(1+Rr\right)\left(1-q\right)}{pp/P} $$

(11)

• $\begin{array}{c}``a"\mathrm{is} \mathrm{the} \mathrm{mole} \mathrm{fraction} \mathrm{of} {\mathrm{H}}_2\mathrm{S} \mathrm{in} \mathrm{feed} \mathrm{gas} =\frac{212.5}{3,306.9}\\ {} =0.0643\end{array}$

• R = mole MEA per mole acid gas absorbed = 3.0

• r = 0.09 mole H₂S per mole lean MEA

Then

$$ \begin{array}{c}A =\frac{0.0643\times \left\{1+\left(3.0\times 0.09\right)\right\}\times \left\{1-\left(2.45\times {10}^{-5}\right)\right\}}{0.33\div 335}\\ {} =82.1\end{array} $$

Therefore

$$ \begin{array}{c}N =\frac{ \log \left\{\left(1\div 2.45\times {10}^{-5}\right)\times \left(82.1-1\right)\right\}}{ \log\;82.1}=\frac{ \log \left(3.283\times {10}^6\right)}{ \log\;82.1}\\ {} =\frac{6.5}{1.91}=3.4\;\mathrm{theoretical} \mathrm{trays}\end{array} $$

Set tray efficiency at 15 %; then actual number of trays = 23 (including reboiler).

MEA has a tendency to foam; therefore set tray spacing at 30 in (1.5 ft).

Then trayed section will have a height of 22 × 1.5 ft = 33 ft.

Calculating the Contactor Diameter

Use foaming factor of 60 %.

Feed gas to the contactor is 30 MMscf/day.

Temperature of gas is 100 °F and its pressure is 335 psia (these are average conditions).

$\begin{array}{c}\mathrm{Then} \mathrm{actual} \mathrm{c}\mathrm{ubic} \mathrm{f}\mathrm{eet} \mathrm{per} \mathrm{s}\mathrm{econd}\left(\mathrm{ACFS}\right) =\frac{30\times {10}^6\times 14.7\times 580}{24\times 3, 600\times 520\times 335}\\ {} =16.41\;\mathrm{c}\mathrm{f}\mathrm{s}\end{array}$

Feed gas in lb/h is 34,722 = 9.645 lb/s.

$$ {\rho}_{\mathrm{v}} =\frac{9.645}{16.41}=0.5881\mathrm{b}/\mathrm{cuft} $$

lb/h of MEA solution is 194,747.

gals/h is 23,317.

And cubic ft/h is 3,117.

Then lb/cuft = 62.48 and at 120 °F (MEA inlet temperature) = 62.1 lb/cuft.

Loading at flood: ${K}_{\mathrm{f}}\surd \left\{{\rho}_{\mathrm{v}}\times \left({\rho}_1\hbox{--} {\rho}_{\mathrm{v}}\right)\right\}$

K _f is 1,280 from Fig. 3 and, inserting a 60 % foam factor, K _f = 768.

Fig. 3

The Brown and Souders flood constant

$\mathrm{Loading}=768\times \surd 36.17=4,619\mathrm{lb}/\mathrm{h} \mathrm{s}\mathrm{q}.\ \mathrm{ft}.$

Let design load be 70 % of flood = 3,233 lb/h∙sq. ft.

$\begin{array}{c}\mathrm{Cross}-\mathrm{sectional} \mathrm{area} \mathrm{of} \mathrm{tray}\left(\mathrm{and} \mathrm{towerI}/\mathrm{D}\right) =\frac{34,722}{3,233}\\ {} =10.74\;\mathrm{s}\mathrm{q}.\ \mathrm{ft}.\end{array}$

Internal diameter of tower (calculated) = 3.7 ft

Call it 4 ft. = 12.6 sq. ft. cross-sectional area.

The actual tray design will be done by others (tray manufacturer) to protect the guarantee requirements.

Calculate the Amine Holdup in the Bottom of the Tower

The minimum liquid holdup will be 1 min from NLL to empty.

$\mathrm{The} \mathrm{volume} \mathrm{of} \mathrm{amine} \mathrm{in}\;1\; \min =\frac{3, 117}{60}=51.95\;\mathrm{cuft}$

$\mathrm{Then} \mathrm{N}\mathrm{L}\mathrm{L} \mathrm{will} \mathrm{be}=\frac{51.95}{12.6} = 4.1\;\mathrm{ft} \mathrm{say}\;4\;\mathrm{ft}$

Then HLL will be set at 8 f. and LLL at 4 f. above tangent.

Add a further 4 f. from HLL to bottom tray.

The Overall Dimensions of the Contactor

The height of the contactor is as follows:

From bottom tangent line:

$$ \begin{array}{ll}\mathrm{T}\mathrm{o} \mathrm{bottom} \mathrm{t}\mathrm{ray}\hfill & =12\;\mathrm{f}\mathrm{t}\hfill \\ {}\mathrm{T}\mathrm{o} \mathrm{t}\mathrm{o}\mathrm{p} \mathrm{absorbing} \mathrm{t}\mathrm{ray}\hfill & =45\;\mathrm{f}\mathrm{t}\hfill \\ {}\mathrm{T}\mathrm{o} \mathrm{wash} \mathrm{water} \mathrm{drawoff}\hfill & =48\;\mathrm{f}\mathrm{t}\left(\mathrm{bottom} \mathrm{o}\mathrm{f} \mathrm{chimney} \mathrm{t}\mathrm{ray}\right)\hfill \\ {}\mathrm{T}\mathrm{o} \mathrm{t}\mathrm{o}\mathrm{p} \mathrm{o}\mathrm{f} \mathrm{wash} \mathrm{section}\hfill & =54\;\mathrm{f}\mathrm{t}\hfill \\ {}\mathrm{T}\mathrm{o} \mathrm{t}\mathrm{o}\mathrm{p} \mathrm{t}\mathrm{angent}\hfill & =58\;\mathrm{f}\mathrm{t}\hfill \end{array} $$

Overall dimensions for the contactor are 4 f. ID × 58 f. Tan-Tan.

Calculating the Heat Balance over the Contactor

The rich gas flow will enter at 100 °F and 320 psig and will have an enthalpy of 350 Btu/lb. Its flow rate is 34,722 lb/h.

The heat of reaction is calculated at 650 Btu/lb of H₂S absorbed.

The lean amine solution enters at a temperature of 105 °F which will be set by heat transfer. The lean product gas will leave at about the same temperature.

The rich amine leaving the contactor is determined by difference

$$ \begin{array}{c}\mathrm{Temperature} \mathrm{of} \mathrm{rich} \mathrm{amine} \mathrm{out} =\frac{23.602\times {10}^6}{\left(38, 949\times 0.663\right)+155, 798}\\ {} =129.95\;\mathrm{say}\;130{}^{\circ}\mathrm{F}\end{array} $$

The Heat Exchanger Design

The hot lean amine stream to the contactor will be cooled from the stripper bottom temperature first by heat exchange against the rich amine leaving the contactor. It will then be trim cooled to the contactor inlet temperature by either water or air. The following is the calculation to determine the size of the lean/rich amine exchanger.

The lean amine from the stripper will be cooled to 175 °F in the heat exchange with the rich amine leaving the contactor. The duty of this exchanger is

$$ \left\{38, 949\times 0.663\times \left(249-175\right)\right\}+\left(155, 798\times 74\right)=13.44\mathrm{MMBtu}/\mathrm{h} $$

The figure 240 °F is a value for the stripper bottom temperature estimated by a quick bubble point calculation of the lean amine at the stripper bottom conditions of temperature and pressure. This will be checked later.

Temperature of the rich amine feed to the stripper (T) is as follows:

$$ \begin{array}{c}\left(23.602+13.44\right) =\left(38,949\times 0.663\times T\right)+155,798\;T\\ {}T =204 {}^{\circ}\mathrm{F}\end{array} $$

The overall heat transfer coefficient for the amine exchanger can be taken as 100 Btu/h sq. ft. °F (this will be checked by the exchanger manufacturer). The exchanger size is

$$ \begin{array}{c}\mathrm{LMTD}\;249\to 175\\ {}204\leftarrow 130=45 {}^{\circ}\mathrm{F}\end{array} $$

$$ \begin{array}{c}\mathrm{Area} =\frac{13,440, 000}{45\times 100}\\ {} =2, 987\;\mathrm{s}\mathrm{q}.\mathrm{ft}.\end{array} $$

The Stripper Design

$\mathrm{Total}\ \mathrm{mol}\mathrm{es}\ \mathrm{of}\ \mathrm{acid}\ \mathrm{gas}\ \mathrm{in}\;\mathrm{feed}=\mathrm{moles}\ \mathrm{absorbed}=212.49\ \mathrm{mol}/\mathrm{h}$

$\begin{array}{c}\mathrm{Residual} \mathrm{acid} \mathrm{gas} =57.37\mathrm{mol}/\mathrm{h}\\ {} \mathrm{Total}\ \mathrm{acid}\ \mathrm{gas}=269.86\mathrm{mol}/\mathrm{h}\end{array}$

$\begin{array}{c}\mathrm{Moles} \mathrm{amine}=637.47\mathrm{mol}/\mathrm{h}\\ {}\left(\mathrm{This} \mathrm{assumes} \mathrm{no} \mathrm{losses}\right)\end{array}$

$\mathrm{Moles}\;\mathrm{water}=8,655 \mathrm{mol}/\mathrm{h}$

$\mathrm{Moles}\;\mathrm{hydrocarbon}\;\mathrm{dissolved}=1.8\ \mathrm{mol}/\mathrm{h}\ \mathrm{a}\mathrm{s}\ \mathrm{C}5$

The Material Balanc e

The material balance over the stripper is given in Table 3.

Table 3 Example of amine stripper material balance

The following calculation establishes the composition of the overhead product and the composition of the liquid reflux stream, thus:

Let x be the moles per hour of water in the overhead product. The H₂S content is established by the total in the feed less the residual H₂S in the bottom product – the lean amine. It is assumed that all the hydrocarbons will leave with the overhead vapor product. The value of x is found by the dew point calculation of the overhead product at the reflux drum conditions of temperature and pressure in Table 4.

Table 4 Example of calculation of overhead product and reflux compositions

The reflux drum conditions were set at 23 psia pressure and 100 °F, and the dew point calculation at these conditions gave a reflux stream composition as shown in Table 4.

• Mole reflux is 2× product vapor.

Tower Top Conditions and Condenser Duty

The tower top pressure shall be the reflux drum pressure plus, say, 3 psi pressure drop over the condenser and about 0.7 psi for piping and other losses. Then the tower top pressure will be 26.7 psia. The total overhead vapor will be product plus reflux as shown in Table 5.

Table 5 Example of calculation of overhead vapor composition

The dew point calculation gave the tower top temperature of 218 °F.

The condenser duty is calculated from the following heat balance over the tower top (refer to envelope 1 in Fig. 4). The heat balance is shown in Table 6.

Fig. 4

Heat balance envelopes for tower overhead

Table 6 Overhead heat balance example

Condenser duty to strip vapors from the feed is 8.125 MMBtu/h. To this will be added the vapor from the reclaimer that has to be condensed. This will be done later.

To Calculate the Internal Reflux from the Top Tray

Knowing the condenser duty, the internal reflux × lb/h can be calculated from the heat balance over the tower top as shown in envelope 2 of Fig. 4. See Table 7.

Table 7 Example of internal reflux from top tray calculation

Solving for x:

$$ \begin{array}{c}9.294+222\;x =0.923+1, 162\;x\\ {}x =8, 905\;\mathrm{lb}/\mathrm{h}\end{array} $$

$$ \begin{array}{c}\mathrm{Mole} \mathrm{weight} \mathrm{of} \mathrm{reflux} =18.5\left(\mathrm{from} \mathrm{the} \mathrm{dew} \mathrm{point} \mathrm{calculation}\right)\\ {}\mathrm{Mole}\mathrm{s}/\mathrm{h} \mathrm{reflux} =481\end{array} $$

The moles of vapor from the reclaimer will be added to this figure when calculating the vapor loading over the top tray. Two trays above the feed tray will be provided as wash trays.

The Stripper Bottom Conditions and Reboiler Duty

The pressure at the bottom of the tower is fixed at 34 psia. This allows a pressure drop of about 0.35 psi per tray which is estimated as a total of 20 trays. The tower bottom temperature is calculated by a bubble point calculation of the bottom product at this pressure of 34 psia (see Table 8).

Table 8 Example of calculation of stripper bottom composition

Enthalpy of bottom product = 230 Btu/lb as liquid.

Calculating the Reboiler Duty

This is determined from the overall tower heat balance as shown in Table 9.

Table 9 Calculation of reboiler duty

Vapor/Liquid on Bottom Tra y

The bottom tray will have a temperature of 240 °F (see Fig. 5 and Table 10). In the following heat balance, let the lb/h of the stripout vapors to the tray be x:

Fig. 5

Tower bottom heat balance loop

Table 10 Bottom tray condition calculation

$$ \begin{array}{lll}x=25, 748\ \mathrm{l}\mathrm{b}/\mathrm{h}\hfill & \mathrm{Mo}\mathrm{l}\mathrm{e} \mathrm{wt}\hfill & =23.08\hfill \\ {}\hfill & \mathrm{M}\mathrm{o}\mathrm{l}/\mathrm{h}\hfill & =1, 115.6\hfill \\ {}\hfill & \mathrm{V}/\mathrm{L}\mathrm{a}\mathrm{t} \mathrm{b}\mathrm{o}\mathrm{t}\mathrm{t}\mathrm{o}\mathrm{m} \mathrm{t}\mathrm{ray}\hfill & =1, 115.6/10,457\hfill \\ {}\hfill & \hfill & =0.107\hfill \end{array} $$

To Calculate the Number of Theoretical Trays in the Stripper

The Kremser equation which is shown graphically in Fig. 6 will be used for this calculation.

Fig. 6

The Kremser equation and correlation

The V/L factor calculated above will be used for this equation. A tower average K value for each component in the feed will also be used. The calculation is shown in Table 11.

Table 11 Estimated number of theoretical trays

Three theoretical trays will achieve the stripping required. Stripping trays have poor efficiency between 12 % and 18 %. Use 15 % in this case; then actual trays will be 3/0.15 = 20 actual trays.

The anomaly for the amount of HC stripped in the above calculation stems from the assumption that the HC is pentane. It is probably a heavier hydrocarbon.

Calculating the Reclaimer Duty and Size

A slip stream of 2 wt% of lean amine solution will be routed through the reclaimer. It will be vaporized to leave a sludge stream of 2 % of the reclaimer feed. The operation will be continuous, and the vapor will be routed back to the tower entering below the bottom tray. The material balance over the reclaimer is shown in Table 12.

Table 12 Reclaimer material balance and heat duty

A typical heat flux over a kettle reboiler is 26,500 Btu/h sq. ft, therefore the area for heat transfer = 80 sq. ft.

The vapor generated by the reclaimer will be added to the vapor load at the bottom tray. Likewise, this amount as liquid will be added to the tray liquid load. The condenser duty will also be increased to accommodate the reclaimer duty. Thus

$$ \begin{array}{c}\mathrm{Total} \mathrm{condenser} \mathrm{duty} =8.125+2.130=10.255\mathrm{MMBtu}/\mathrm{h}\\ {}\mathrm{Vapor} \mathrm{l}\mathrm{o}\mathrm{ad} \mathrm{t}\mathrm{o} \mathrm{b}\mathrm{o}\mathrm{t}\mathrm{t}\mathrm{o}\mathrm{m} \mathrm{t}\mathrm{ray} =\mathrm{stripout}+\mathrm{reclaimed} \mathrm{vapor}\\ {} =25, 748\ \mathrm{l}\mathrm{b}/\mathrm{h}+2, 851/\mathrm{h}\\ {} =28, 599\ \mathrm{l}\mathrm{b}/\mathrm{h}\\ {}\mathrm{M}\mathrm{o}\mathrm{l}/\mathrm{h} =1, 115.6+135.8\\ {} =1, 251.4\end{array} $$

Stripper Tower Dimensions

As in the case of the contactor, the cross-sectional area of the stripper will be calculated using the Brown and Souders method as follows:

Cross-sectional area of the tower will be based on the loadings over the bottom tray; thus

$$ \begin{array}{ll} \mathrm{Total} \mathrm{vapor} \mathrm{t}\mathrm{o} \mathrm{t}\mathrm{ray}\hfill & =1, 251.4 \mathrm{mol}/\mathrm{h}\hfill \\ {}\mathrm{In} \mathrm{actual} \mathrm{cubic} \mathrm{feet}/\mathrm{s}\hfill & =\frac{1, 251.4\times 378\times 700\times 14.7}{520\times 34\times 3,600}\hfill \\ {}\hfill & =76.47\;\mathrm{ACFS}\hfill \\ {} {\rho}_{\mathrm{v}}=7.85/76.47\hfill & =0.104\mathrm{lb}/\mathrm{cuft}\hfill \end{array} $$

$$ \begin{array}{c}\mathrm{Total} \mathrm{li}\mathrm{q}\mathrm{uid} \mathrm{from} \mathrm{the} \mathrm{bottom} \mathrm{tray} =\mathrm{stripout}+\mathrm{product}+\mathrm{reclaimer} \mathrm{l}\mathrm{i}\mathrm{q}\\ {} =25, 748+196, 482+2, 851\\ {} =225, 081\mathrm{lb}/\mathrm{h}\end{array} $$

$$ \begin{array}{c}\mathrm{lb}/\mathrm{gal} \mathrm{of} \mathrm{liquid} \mathrm{at}\;240 {}^{\circ}\mathrm{F} =7.87\\ {}\mathrm{Gals} \mathrm{per} \mathrm{hour} =28, 600\;\mathrm{and}\;\mathrm{cubic} \mathrm{ft}/\mathrm{h} \mathrm{is}\;3, 823\\ {}{\rho}_1 =58.87\mathrm{lb}/\mathrm{cuft}.\end{array} $$

Loading at flood $={K}_{\mathrm{f}}\surd \left\{{\rho}_{\mathrm{v}}\times \left({\rho}_1\hbox{--} {\rho}_{\mathrm{v}}\right)\right\}$

From Fig. 5 K _f = 1,280 and at 60 % = 768

$$ \begin{array}{c}\mathrm{Then} \mathrm{loading} =768\times 2.47\\ {} =1, 899\mathrm{lb}/\mathrm{h} \mathrm{s}\mathrm{q}.\;\mathrm{ft}.\end{array} $$

Let loading be 80 % flood = 1,519:

$$ \begin{array}{c}\mathrm{Cross}-\mathrm{sectional} \mathrm{area} =\frac{28, 599}{1,519}\\ {} =18.8\;\mathrm{s}\mathrm{q}.\mathrm{ft}.\\ {} \mathrm{and} \mathrm{diameter}=4.9\;\mathrm{ft} \mathrm{call} \mathrm{it} 5\;\mathrm{ft} \mathrm{or}\;19.6\;\mathrm{s}\mathrm{q}.\;\mathrm{ft}.\end{array} $$

Tower will contain 20 valve-type trays made up of 18 stripping trays and 2 rectifying trays. As in the case of the contactor trays, they will be spaced at 30 in. Trayed section will therefore be 19 × 30 in. = 570 in or 47 f. 6 in. from bottom to top tray.

The bottom of the tower (from bottom tray to bottom tangent) will be sized to cater for a 2 min holdup of liquid to the HLL. Thus

$$ \begin{array}{c}\mathrm{Total} \mathrm{liquid} \mathrm{from} \mathrm{bottom} \mathrm{reboiler} =196, 482+2, 851\\ {} =199, 333 \mathrm{lb}/\mathrm{h}\end{array} $$

$$ \begin{array}{ll}\mathrm{lb}/\mathrm{gal}\ \mathrm{at}\ 60 {}^{\circ}\mathrm{F}=8.35,\;\mathrm{and}\;\mathrm{at}\ 249 {}^{\circ}\mathrm{F}\hfill & =7.89 \mathrm{lb}/\mathrm{gal}\hfill \\ {}\mathrm{Then}\ \mathrm{gal}\mathrm{s}/\mathrm{h}\ \mathrm{of} \mathrm{total} \mathrm{bottoms}\hfill & =199, 333/7.891\hfill \\ {}\hfill & =25, 264 \mathrm{gal}/\mathrm{h}\hfill \\ {}\hfill & =421\;\mathrm{G}\mathrm{P}\mathrm{M}\hfill \end{array} $$

or 56.3 cubic ft/min

Volume resident over 3 min = 168.9, say, 169 cubic ft.

Height of HLL = 8.6; allow 4 f. from HLL to bottom tray.

Summary of stripper height (all dimensions from bottom tangent)

To bottom tray	12 f. 6 in.
Trayed section	47 f. 6 in.
Top tray to top tangent	4 ft
Total height	64 ft

There will be a 15 f. skirt to give the total height above grade of 79 ft.

This completes the process design of the major items of equipment. These and the smaller items of equipment are shown in the following preliminary process flow sheet Fig. 7.

Fig. 7

The preliminary process flow sheet for a MEA treating plant