12.

2 Design Method
The tank dimensions are determined according to standard tank
geometries as used by the Denver Company (United States). Tank
shell thickness is sized according to the limitations imposed by the
Australian design standard for pressure vessels (AS1 210; Ref. Tl ).
The tank contents are non-flammable but highly toxic and corrosive,
appropriate safety features are recommended. Details of the
calculations are given in Appendix J.

J.

l Introduction
This appendix contains the calculations related to the specification of
the nitric acid product-storage tank.
The tank should have the capacity to store one week of full
production, this allows continued production in the event of
unscheduled shutdowns in the adjacent ammonium nitrate plant.
This minimum capacity of 1500 m3 should also prove adequate to
handle any external nitric acid sales.
The tank must be constructed of stainless steel type 304L (‘nitric
acid grade’), the specification of this material is given in Appendix D.
The design data for this unit are specified in Table 12.1. The design
tank capacity is 2000 m3, corresponding to the standard tank size as
supplied by the Denver Company (USA). The extra capacity
allowance ensures that the tank is not filled beyond 80% of the total
height, thus avoiding any problems of tank overflow or ‘roll-over’.
The design temperature represents the maximum for process-acid
feed. The working pressure represents atmospheric pressure plus
acid-vapour pressure at the design temperature.

5.2 Tank Dimensions

The tank dimensions required for this capacity are predetermined by
selection of a standard tank configuration. The nearest tank sizing of
this capacity has an inside diameter of 15.2 m (50 ft.) with a tank
height of 10.7 m (35 ft.) This gives a tank capacity of 1950 m3.
The minimum wall thickness required to support the weight of the
contained acid and the roof structure is determined using the formula
338
APPENDIX J 339
given in the Australian design code AS 1210 (Ref. Tl ; p-76) for the
specification of pressure vessels.
Thick-walled cylindrical and spherical shells (internal
pressure), minimum thickness based upon circumferential
stress (longitudinal joints)
t = (D,/2) (Z”.5 - 1) = (D,/2) [(Z”.5 - 1 )/Z”.5]
where
t = wall thickness (mm);
Q = tank inside diameter (mm);
DO = tank outside diameter (mm);
Z = (FE + P)/(FE - P);
F = design tensile strength of material (MPa);
E = joint efficiency;
P = internal pressure (MPa).
The internal pressure is equivalent to the head of liquid inside the
tank. This maximum head of 10.7 m represents a pressure of 142 kPa.
The recommended wall thickness is:
Z = (FE + P)/(FE - P)
=[(108 x 0.8) + 0.142]/[(108 x 0.8) - 0.1421
= 1.003
t = (15 200/2) (1 .003°.5 - 1) = 11 mm
Adding a corrosion allowance of 5 mm, the final recommendation is
for 16 mm plating for the tank shell based on circumferential stress.

Minimum thickness based upon longitudinal stress

(circumferential joints)
Formula as given above for circumferential stress, except that:
Z = [P/(FE)] + 1.
With the internal pressure at 140 kPa, the calculation is:
Z = [P/(F E)] + 1
= [0.140/(108 x 0.8)] + 1
= 1.0016
t = (15 200/2) (1 .OOl 6°.5 - 1)
=6mm
3 4 0 APPENDIX J
This indicates that circumferential stresses are more important, and
they determine the minimum shell thickness for this tank. The BHP
steel plate available and closest to this specification (Ref. T2) is
16 mm thickness.
Checking Calculations for Other Stresses
Dead- weight stress
Volume of metal = Tank shell + Tank roof
= [z{l5.2 + (2 x 0.016)} 0.016 x 10.71 + 1.3 [(r /4) 15.2* x
0.0161 = 12 m3
Density of SS304L = 7.8 tonnes/m 3
Mass of tank = Volume x Density
= 12 x 7.8
= 93.6 tonnes
Considering the stresses:
Weight stress = m g (K D, t,)
= (93.6 x 9.8)/( ar15.2 + (2 x 0.016)) 0.016)
= 1200 kPa
= 1.2 MPa
Axial stress = P D,/(4 J ts)
= 0.140 {I 5.2 + (2 x 0.016)}/ (4 x 1 .O x 0.016)
= 33 MPa
Hoop stress = 2 x Axial Stress
= 66 MPa
Wind stresses are disregarded because of the high ratio of tank
diameter to tank height.

Analysis of Stresses
Up wind Total stress = Axial stress - Radial stress
= 33 - 1.2
= 31.8 MPa
Downwind Total stress = Hoop stress - Radial stress
= 66 - 1.2
= 64.8 MPa
APPENDIX J
Radial Radial stress = 0.5 x P = 70 kPa
Maximum stress = 70 MPa
341
The maximum stress is approximately 35% below the design stress of
108 MPa, and therefore the shell thickness used in this design is
considered acceptable.
inlet/Outlet Line Diameters
The inlet and outlet line diameters are sized for a recommended liquid
flowrate of 2 m/s (Ref. T3; p.163).
(a) /n/et line The inlet line sizing is determined by allowing 20%
above the normal product flowrate of 11 700 kg/h. This corresponds
to a volumetric flowrate of 2.9 X 1 Om3 m3/s.
Area of pipe = Volumetric flowrate/Velocity
= 2.9 x 10-312
= 1.44 x 10-3m2
Diameter of pipe= [Area x 4/ X]‘.~
[1.44 x 1o-3 x 4/7rp5
= 40mm
The nearest commercial pipe size (Ref. T4; Table 6.6) is a nominal
pipe size of 1.5, schedule number 40s (with inside diameter of
41 mm and a wall thickness of 4 mm).
(6) Out/et line The outlet flowrate is calculated based upon the need
to fill a standard 30 tonne tanker in 15 minutes. This corresponds to a
volumetric flowrate of 2.5 x 1 O-* m3/s

Area of pipe = Volumetric flowrate/Velocity

= 2.9 x 10-312
= 1.44 x 10-3m2
Diameter of pipe= [Area x 4/ X]‘.~
[1.44 x 1o-3 x 4/7rp5
= 40mm
The nearest commercial pipe size (Ref. T4; Table 6.6) is a nominal
pipe size of 1.5, schedule number 40s (with inside diameter of
41 mm and a wall thickness of 4 mm).
(6) Out/et line The outlet flowrate is calculated based upon the need
to fill a standard 30 tonne tanker in 15 minutes. This corresponds to a
volumetric flowrate of 2.5 x 1 O-* m3/s
Area of pipe = Volumetric flowrate/Velocity
= 2.5 x IO-‘/2
= 1.23 x lo-*m2
Diameter of pipe= [Area x 4/ 7r]“.5
= [1.44 x 1o-3 x 4/@5
= 40mm
The nearest commercial pipe size (Ref. T4; Table 6.6) is a nominal
pipe size of 6, schedule number 120 (with an inside diameter of
140 mm and a wall thickness of 14 mm).
J.3 Mechanical and Safety Features
A standard metal staircase and railing should skirt the outer edge of
the tank providing access to the tank roof. A manhole in the tank roof
3 4 2 APPENDIX J
provides access for any internal repairs. Discrete inlet and outlet lines
are required to feed into the base of the column.
A pressure relief valve is attached to the roof. This valve is opened
automatically when pumping product to, or withdrawing product
from, the tank. The valve shuts when pumping stops so that vapour
losses from the tank are contained. A bursting disc on the roof also
provides emergency pressure relief for sudden pressure rises. The
final tank specification is summarized in Table 12.1.
5.4 Tank Cost
The cost of this tank is estimated from Ref. T4 (Figure 6.142). The
tank base cost is estimated according to the size, material of
construction and plate thickness used.
The base cost from Ref. T4 is USS225 000. These calculations are
based upon 1979 United States figures and must be adjusted for both
inflation and currency differences. The M & S equipment index (Ref.
T5; p.7) is used, therefore:
Final tank cost = 225 000 (786.0/745.6)(1/0.61)
= As390 000

T1

5.4 Case Study - Site Considerations

Summary
Nitric acid and the nitrogen oxide gases present in the process are
highly toxic. It is imperative that the choice of site selection and plant
layout reflects the potential hazard from both of these sources.
The nitric acid plant will be part of a chemical plant complex that
will include an ammonia plant, a nitric acid plant and an ammonium
nitrate plant. Consideration is given to the needs of all three of these
plants in the site selection procedure.
The site chosen for the nitric acid plant, as a part of the larger
chemical plant, is a 10 hectare plot in the Bunbury district of Western
Australia. The site is located between the port handling facilities (for
alumina) belonging to Alcoa of Australia Ltd, and Leschenault Road.
The site runs parallel to the Preston River and is less than 1 km from
the main port area. It features easy port access, adjacent rail facilities,
and an abundance of river water (for process cooling purposes).
The layout suggested for the chemical plant complex includes a
central control room to operate all three plants. Administration,
laboratory, and workshop areas are also common. The nitric acid
plant is small, occupying less than 1 hectare. There is space on the 1
hectare plot for inclusion of a second parallel process train for
possible future expansion.
Normal operation should be well within the environmental
regulation limits set by the EPA. Liquid waste is virtually non-existent
and can be sent to the normal sewerage drains. Any acid spills should
be diluted. Tail-gas emissions are thought to be less than 1000 ppm
of nitrogen oxides (about half the current EPA limit). Should tail-gas
emissions exceed this figure, then a catalytic combustor would be
necessary to reduce nitrogen oxide levels to below 400 ppm.
References Used
General Introduction: G8.
7 6 CHEMICAL ENGINEERING DESIGN
5.4.1 Site Considerations - Introduction
There are several aspects to be considered regarding the siting and
operation of the nitric acid plant. First, a suitable site must be chosen
and second the plant layout must be planned after the site
characteristics are assessed. Finally, an environmental impact
analysis needs to be performed to ascertain the expected effect of the
plant and the chemicals on the surrounding areas.
5.4.2 Site Selection
There are a number of considerations concerning the choice of site
locations for a new nitric acid plant within Western Australia. Some
of these are general considerations whilst others relate directly to the
process and its requirements. Those considerations relevant to this
study include:
(a) Close proximity to the anticipated market.
(b) An availability of fundamental infrastructure (including port
facilities and both rail and road access).
(c) Utility costs and availability.
(d) A suitable local labour force.
In the determination of a site location for this nitric acid plant, a
broader spectrum of factors must be considered. This plant will
almost certainly have to be part of a larger chemicals complex
involving the production of ammonia (for nitric acid plant feed) and
ammonium nitrate (to use most of the nitric acid product). A site of
about 10 hectares is required.
After assessing all these factors, there are several possible options
for the site location. These include a series of industrial belts within
the Perth metropolitan region and three regional centres (Bunbury,
Geraldton and Karratha). Figure 5.1 shows the location of these areas
within Western Australia. Both metropolitan and country areas offer
promising initial opportunities. These are now investigated in more
detail.