6.0 Control Equipment Cost

 

Economics are always an issue in engineering practice. In a typical project, we incur expenses and acquire revenues over time, and we face the challenge of determining the best project decisions, where best means achieving the highest net profit.  Fortunately, methods for economic analysis are readily available.  These methods consider the time-value of money and provide appropriate measures of profitability, such as net present value (NPV).  The methods for economic analysis are presented in many excellent textbooks, for example, Blank and Tarquin (2002).

Engineers are responsible for estimating the benefits and costs of a project.  The benefits accrue from improved operation that improves product quality, increases reactor selectivity and separator recovery, increases production rates, reduces fuel consumption, and reduces undesirable effluents.  The approaches and calculations for determining the benefits depend upon the specific project.  General approaches and example data and calculations are available in, among others, Marlin et. al. (1987) and Shunta (1995).

 

            This section presents some useful information for estimating the cost of control equipment.  We must recognize the cost includes the following components.

 

·                     Purchase

·                     Transportation from supplier to user

·                     Installation and documentation

·                     Calibration

·                     Maintenance over the equipment lifetime

 

Some typical purchase costs are given in this section.  Transportation cost clearly depends on the particular item and supplier.  Installation includes the wiring, power, and programming any associated computing equipment.  Calibration includes checking that the proper signal is connected to the desired computing element and ensuring that standard signals evoke the desired result, e.g., a temperature at the sensor provides the correct reading for display, alarm and control.  Maintenance includes the cost of personnel and spare parts.

 

            Typical purchase costs are given in Tables 6.1 to 6.3 at the end of this section.  Most of this data has been provided by Liptak (2003; Liptak, 1999), who provides much valuable detail about each item.  Proper cost estimation requires that the equipment matches the process requirements, which requires careful evaluation of equipment performance.  Therefore, reference to Liptak (2003) and to suppliers’ data is strongly recommended when performing cost estimations.  However, the following typical data can be helpful for educational purposes and for quickly screening many potential projects.

 

            In addition, we must recall that prices are a commercial decision negotiated between purchasers and suppliers.  We expect that an order of many components will have a lower unit price than an order of one or a few components.  The data below is typical for unit purchases.

 

            Finally, engineers use “quick and dirty” approximate estimates when initially evaluating many projects.  These methods are not very accurate, typically having uncertainty of ±30% or more.  An example that is often needed is the cost of all instrumentation, including installation, for a plant construction project.  Estimates are available (e.g., Perry’s Handbook, 1997); however, the technology and costs have been changing rapidly, especially since the introduction of fieldbus digital communication.  Therefore, caution must be used when applying correlations based on old technology, often from the 1960’s.

 

 

Table 6.1 Sensors (conventional technology with transmitter, additional cost for “smart” features to be compatible with fieldbus technology)

Process variable

Cost

(US$ in 2003)

Comments

Flow - orifice

500-3500

Flange connections, 2-12 in pipe

Flow - pitot and similar

1000-2000

Calibration costs extra

Flow - mass

1500-7000

1 in. pipe, cost depends strongly on sensor technology

Flow - positive displacement

3000-5000

1500 SCMH

Flow - turbine

3000

2-3 in. pipe, cost depends strongly on pipe size

Flow - venture/nozzle

500-1000

6 in. pipe, costs vary depending on sensor type and materials of construction

Temperature - thermocouple

200

Cost includes thermal well.  With transmitter could cost up to $2000

Temperature - RTD

100-250

Cost includes thermal well.  With transmitter could cost up to $2000

Temperature - thermister

See RTD

 

Temperature - optical pyrometer

500-5500

Thermal imaging much more expensive

Temperature - bimetalic

65

For local display only

Pressure - bourdon

300

Local indication

Pressure - electronic

1000-4000

Many technologies (See Liptak, 2003)

Level - pressure difference

1500

Local indicators few hundred dollars

Level - float

2000-5000

Switch or local indicator lower cost

Level - displacement

2500

 

Level - Laser

4000-6000

 

Level - Radar

1500-5000

 

Level - Ultransonic

650-2500

 

Analyzer - sampling system

3500-7000

Single sample stream

Analyzer - installation

--

Varies depending upon the location, safety requirements, and analyzer technology

Analyzer

--

Must determine the cost for each analyzer type individually

 

 

Table 6.2 Controllers

Controller

Cost

(US$ in 2003)

Comments

Temperature - regulators

400-1000

 

Pressure - regulators

150-3000

Depends on pipe size and technology

Flow - regulator

250-1750

 

Controller, electronic or digital

500-6000

Depends on flexibility in algorithms and number of controllers in single digital controller

Controller - pneumatic

1000-2500

 

Distributed Digital Control System

--

See Liptak (1999) for a sample cost estimate for an integrated system

 

Table 6.3 Final elements

Final Element

Cost *

(US$ in 2003)

Comments

Actuator

--

Cost included in valve cost

Ball valve body

2000

4 in piping

Butterfly body

2000

       ²

Globe valve body

3000

       ²

Diaphragm valve body

300-600

       ²

Accessories - positioner

600

       ²

Accessories - handwheel

500

Maximum cost

Accessories - limit switch indicator

50-150

 

*  Note that all valve costs depend on the pipe size, materials of construction, etc.  See Liptak (1999) and other resources for correlations of cost vs. pipe size and materials of construction.