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Some Utility Consumption Estimates




Some Utility Consumption Estimates 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:

1 Instrument 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 5.5°C (10°F) 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.
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.
very nicely compiled Ankur...thks a lot
Thanx Ankur

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
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Qalander (Chem)
Feb 21 2012 11:57 PM
Dear Congratulations!
Good info;seems reliable to fairly estimate in practical way.
Thanks.
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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.
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
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 the compressor

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

Regards,
Ankur
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
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christopher.choa
Feb 18 2014 03:52 AM

Basically, only 2-3 of the safety shower is assumed working simultaneously in a plant even though there are many installed.

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