intrument air consumption

7/28/2019 Intrument Air Consumption

1/4

As part of preparing a process discipline manual for one of my previous organizations, one section that I had prepared was

"Guidelines for Preparation of Utility Summary". This document besides containing an excel template for utility summary also

had some guidelines for determining the consumption of utilities such as instrument air, cooling water make-up, potable water

and water requirements for a safety shower. I am reproducing some information:

1Instrument Air Requirement

The following guidelines may be adopted for estimating instrument air consumption for different types of pneumatic

instruments:

- Control Valves with diaphragm actuator and positioner and I/P converter-2.0Nm3/h

- Control (generally on-off type) valves with piston actuator and positioner 5 Nm3/h 10% of this consumption will be

considered in calculations.

The estimated total instrument air quantity should be multiplied by 1.3 to account for uncertainties in the data used for the

estimate and to allow the installation of additional instruments during the early years of plant operation.

2 Cooling Tower Make-up

-Evaporation Loss: Approximately equal to 1% of circulation rate for each 5.5C (10F) of cooling tower temperature range.

- Drift Loss: 0.1 % of circulation rate as a preliminary estimate.

- Blowdown: This quantity is dependent on circulation rate, range, and cycles of concentration

Total Make-up water = Evaporation Loss + Drift Loss + Blowdown

3 Potable Water Requirement

As a conservative estimate a figure of 150 litres per day per person should be considered for preliminary calculations for

potable water. This includes water for drinking and sanitation.

4 Safety Shower

Water quantity requirement for safety showers to be considered based on each safety shower operating for 15 minutes per day.

A minimum flow rate of 4.5 m3/h for each safety shower is recommended as per ANSI Z538.1. As an example if there are 10

safety showers required to be installed for the project, then the water requirement may be calculated as follows:

Quantity required per day per safety shower = 4.5 x (15/60) = 1.125 m3/day

No. of showers = 10

Total water quantity for safety showers for the project = 10 x 1.125 = 11.25 m3/day

Other utilities such as Fuel Gas, Nitrogen, Steam etc. are not considered because they cannot be generalized and require

specific consumption calculations depending on the project / plant requirement.

Let me hear comments from the knowledgable members and readers of "Cheresources".

Regards,

Ankur.

Point No. 1, 2 & 3 are almost tallying with my figures. I do not have idea on Safety Shower.

icingrock

Feb 21 2012 06:36 PM


2/4

Control (generally on-off type) valves with piston actuator and positioner 5 Nm3/h 10% of this

consumption will be considered in calculations

I don't have experiences with design of utilities so my question could be not heavy.What do you

mean by 10% of 5 Nm3/h should be considered in calculations.If 0.5 Nm3/h should be considered for

calculation, what about the other 4.5 Nm3/h.

sameerjb

Feb 21 2012 09:56 PM

very nicely compiled Ankur...thks a lot

debasisq8

Feb 21 2012 11:18 PM

Thanx Ankur

ankur2061

Feb 21 2012 11:21 PM

'icingrock', on 22 Feb 2012 - 06:46 AM, said:

Control (generally on-off type) valves with piston actuator and positioner 5 Nm3/h 10% of this

consumption will be considered in calculations I don't have experiences with design of utilities so my

question could be not heavy.What do you mean by 10% of 5 Nm3/h should be considered in

calculations.If 0.5 Nm3/h should be considered for calculation, what about the other 4.5 Nm3/h.

On-off valves are either in open or closed position as required by the process. In any of these static

positions, on-off valve will not consume any instrument air except for leakage losses from the

cyclinder which is negligible. Thus of the total on-off valves in the plant, operation of 10% of them

simulataneously can be considered conservative enough to include in instrument air calculations.

This is the logic behind the statement that "10% of this consumption will be considered in

calculations"

Hope this helps.

Regards,

Ankur


3/4

Qalander (Chem)

Feb 21 2012 11:57 PM

Dear Congratulations!

Good info;seems reliable to fairly estimate in practical way.

Thanks.

Robert Montoya

Feb 22 2012 03:22 PM

Dear Ankur; is important take into account in the instrument air 30% due the consumption during

the regeneration of air dryer tower.

Zack Adam

Apr 16 2012 11:10 AM

Dear Ankur;

For the item 1

Some considered (10%-15% Margin for Control Valve + Continuous IA users) x 1.3 (30%

uncertainties) + Max Intermittent User

For the Intermittent users, some call for 3 biggest SDVs

May I know what are the continuous air consumers that normally considered in IA Receiver

calculation?

any comments

ankur2061

Apr 16 2012 11:53 AM


4/4

Zack,

IA receiver is sized on a hold-up time of 10-15 minutes from maximum pressure to min. pressure

(say 8.5 barg to 4.5 barg) considering the maximum consumption and no air supply from thecompressor

Continuous IA users in a plant are diaphragm type modulating control valves.

Regards,

Ankur

RAJIV JAIN

May 11 2012 12:03 PM

dear ankur can u pls tell what is the compree

sed air 4kg/cm2g for a ods pump for acidic slurry 10m3/hr 10m head

intrument air consumption

Documents