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Sulphuric Acid on the WebTM Technical Manual DKL Engineering, Inc.

Knowledge for the Instrumentation - Acid Concentration

Sulphuric Acid January 4, 2017

Industry
Introduction Associated Links
Conductivity
Sulphuric Acid on the Refraction
Sound Velocity
Web
Recommended Methods
Instruments
Introduction
General
Equipment Suppliers
Contractor Introduction
Instrumentation
Industry News
The on-line continuous measurement of sulphuric acid/oleum is based on the fact
Maintenance
Acid Traders that a physical property will change as the concentration changes. Properties such
Organizations as conductivity, refractive index and sound velocity are typically used to measure
Fabricators sulphuric acid/oleum concentrations. The recommended methods of measurement
Conferences
Used Plants
over the whole range of sulphuric acid and oleum are given below.
Intellectual Propoerty
Acid Plant Database Conductivity
Market Information
Library
Electrical conductivity is a property of a fluid that can be used to determine its
concentration. The graph below shows the conductivity (micromhos) at 25ºC for
Technical Manual several different fluids, including sulphuric acid from 0 to 100%wt. The vertical axis
ranges from 0 to 900,000 micromhos.
Introduction
General
Definitions For sulphuric acid, the conductivity varies such that for a given conductivity there
Instrumentation could be more than one concentration. This makes conductivity unsuitable for
Plant Safety
measurement over the full range of acid concentration (i.e. 0 to 100% H2SO4).
Metallurgial Processes
Metallurgical However, conductivity can be used where the concentration will vary over a small
Sulphur Burning range and where the range will not cross over one of the peaks or valleys of the
Acid Regeneration
Lead Chamber
conductivity curve.
Technology
Gas Cleaning
Contact
Strong Acid
Acid Storage
Loading/Unloading
Transportation
Sulphur Systems
Liquid SO2
Boiler Feed Water
Steam Systems
Cooling Water
Effluent Treatment
Utilities
Construction
Maintenance
Inspection
Analytical Procedures
Materials of Construction
Corrosion
Properties
Vendor Data

DKL Engineering, Inc.

Handbook of Sulphuric Acid

Manufacturing
Order Form Refraction
Preface
Contents
The refraction of light
Feedback
through sulphuric
Sulphuric Acid Decolourization acid will depend on
Order Form the temperature and
Preface concentration. This
Table of Contents
property can be used
to determine the
Process Engineering Data
Sheets - PEDS concentration of
Order Form sulphuric acid.
Table of Contents
Introduction
Energy radiated from
Bibliography of Sulphuric Acid
a LED passes

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Technology through the prism surface to be reflected off a

Order Form
mirror to the prism-to-process interface. The
Preface
Contents light reaching this interface intersects the
same interface over a series of angles chosen
Sulphuric Acid Plant to include the critical angle (Ic) for the process
Specifications being measured. Light intersecting the
interface at an angle greater than the critical
angle is refracted into the solution. Light
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intersecting the interface at less than the
critical angle is reflected up to a mirror and out
of the prism up to the charge coupled device
(COD) linear array to be scanned.

The image seen by the CCD is composed of

simple light and dark periods. As the refractive index of the process changes, the
change in critical angle, changes the ratio of light to dark periods as seen by the
CCD. This time period change is further enhanced and displayed as a reading in
refractive index.

Sound Velocity

The velocity of sound in sulphuric acid/oleum can be used to determine the acid
concentration. The first graph illustrates the variation of sound velocity with acid
concentration (0 to 100% H2SO4) and second graph illustrates the same
relationship except for oleum.

The nature of sound velocity in sulphuric acid makes this property ideal for
determining acid concentrations in the range of 60 to 100% H2SO4. Calibration of
the instrument is done by comparison with acid of known concentration.

The velocity of sound in sulphuric acid/oleum is affected by the presence of

bubbles and cleanliness of the acid. The sample must be drawn off in such a
manner as to avoid entrainment of bubbles and foreign matter which will affect the
accuracy of the measurement.

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Recommended Methods

The recommended methods of measurement over the whole range of sulphuric

acid and oleum are given in the following table.

Sulphuric Acid Oleum

Recommended Method
%H2SO4 % Oleum
0-25% - Conductivity
35-75% - Conductivity
60-100% - Sound Velocity
Conductivity, Sound
95-100% -
Velocity
100-107.875% 0-35% Sound Velocity
107.875-122.5% 35-100% Sound Velocity

Instruments

Type Range Manufacturer Model No. Remarks

Conductivity
Accuracy: ± 0.05 wt%
and Sound - SensoTech GmbH LiquiSonic
Brochure
Velocity

Conductivity 0-25% Foxboro Trans: 870EC-TF49F

H2SO4 Sensor: 871EC-TF2-V Temperature compensation required
35-75% Mtg Flg: 51191/EP129A (2")
H2SO4
95-100% Rosemount Model 222 Toroidal Conductivity Maximum Temperature: 182ºC
H2SO4 Maximum Pressure: 125 psig
Connection: 1" or 2" - 150 lb Flange
Temperature compensation required

Refraction - The Electron-Machine Corp.

MPR E-Scan Accuracy: ± 1% of span or 0.000075
Refractive Index (RI) whichever is
greater
Span: 0.0015 RI minimum, 0.132 RI
maximum
Temperature: up to 150ºC (300ºF)

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Mounting:

Products: Range: Measurement range covers

0-100 % by weight (Refractive Index
Probe Process Refractometer nD 1.3200 – 1.5300).
PR-43-GP
Remarks: Reliable and accurate
product based on digital sensing
technology; even large amounts of
suspended solids, bubbles or color
changes do not affect the
measurement or the accuracy. The
accuracy is ±0.1 % b.w. and the
measurement is automatically
temperature compensated. The
technology allows configuring low and
high concentration alarms. Intrinsically
safe and hazardous area certification
is provided for hazardous areas.
Compact Process Refractometer Special wetted parts materials such
PR-43-GP, as AISI 904L stainless steel, Alloy 20,
Hastelloy C-276, Nickel 200 and
Saunders Body Refractometer
Titanium ASTM B348.
PR-23-W
Process temperature range: -20°C -
Teflon Body Refractometer
150°C / -4°F – 302°F.
PR-23-M,

Refinery Probe Process

Refractometer PR-23-RP.

Sound 60-100% Nusonics Model 86 Sonic Concentration Accuracy: ± 0.1wt% for 90-100%
Velocity H2SO4 Mesa Labs Monitor H2SO4
Range: 500-3000 m/s
Sensor: HSX/T Temperature: -15 to 185ºC

Application Note

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