7 replies to this topic

[trilok_sontakke]

Dear All

anybody has spreadsheet/program for designing of chilling plant.

which should give

1. TR calculation
2. pump capacities





Thanks
Trilok

[trilok_sontakke]

I have determined refrigerant volume required and pump flow required.

please see the spreadshhet and add your valuable comments.

I need guidelines for determining compressor design and heat exchanger design in chilling plant.

Thanks
Trilok  chilling_plant.doc   83.5KB   356 downloads

[Art Montemayor]

Trilok:

Your post is very misleading and lacking in giving a clear indication of just what exactly your scope of work is and what is it that you specifically need. To request guidelines is very vague for a posting in the industrial forum. I am going to approach this as if it were meant for the student forum because it borders on the basic question of how to do a design. Allow me to explain what is confusing about this post:

You initially say you want a spreadsheet for designing a chilling plant and it should give the “TR” and pump capacity calculation. You don’t define what “TR” is, but I suppose it is meant to mean “Tons of Refrigeration”. This should be identified in order to avoid confusion and acronym differences across national lines. Calculating the cooling loads and pump capacities is straight-forward and every engineer should be able to set up his/her own spread sheet. You don’t even give us the basics: Are you using brine? If so, what brine? Are you using mechanical refrigeration? If so, what type? What refrigerant?

You say you attach a spreadsheet. However, it turns out to be word processing tables that reveal no identification or formulas employed nor what the titles represent. These tables are next to useless. They seem to be calculations of “line pack” – i.e., the volume held by the piping and equipment. This type of information is of no importance and is not required to calculate what you seem to be after.

I’m going to try to attach an Excel workbook to this thread in order to show clearly what I mean and to show you even more clearly what has (or should) to be done to identify the basic needs of a brine chilling operation and system. I apologize for the poor Excel graphics. I cut and pasted some of them from another spreadsheet and failed to really do a professional job on the PFD. I can do much better than that on Excel. However, it should suffice to show you what can – and should – be done in making engineering calculations that anybody can easily understand and review.

Your first step is a simplified Process Flow Diagram (PFD) in order to identify the type of process you intend to employ and the quanity and type of major equipment involved. To this, you attach your process thermal and flow conditions after making heat and mass balances.

Note that my PFD shows a 2-stage ammonia refrigeration system. I don’t know what your refrigeration needs are, but this should be more than ample. If you only need a single-stage refrigeration system, then you can easily erase the 2nd stage compressor and intercooler. The important thing to note is that you should always document your work product. Note that each engineering calculation or work product is identified for author, date done, Revision # and rev. date, Page of which page, File ID, and where to find it within the file. All the work product that you produce should be clearly identified and organized in order to be prepared to defend your decisions and results. You will regret doing otherwise – believe me.

As you can see, you build up and construct your calculation worksheet according to your specific application and needs. This is very easy to do for a chiller process. It only involves Unit Operations, so the calculations are all very direct and simple to apply. I don't believe you need instructions on how to make a mass or heat balance. But if you do, you can now specifically identify or point to a place in your process where you need this assistance or help.

I hope I succeed in attaching the workbook and that this helps point you in the right direction.
If I don't succeed in attaching the workbook, write me an email and I'll send it to you.

Art Montemayor
 Brine_Chilling.zip   10.52KB   432 downloads

[trilok_sontakke]

Dear Art

Thanks for the reply.and thanks for being straightforward.

As you are saying that my attached file is of no use to others which is true,this is because it is based on equipments from my industry whose details I have not provided.

Leaving away the attached file, What I have done is I have calculated total volume of all reactor jackets,pipings,heat exchanger jackets whereever the brine is going.This gives me tank volume required in chilling plant.
Also I have taken velocity of brine in each pipe as 2 m/s and line size of 2 inches connecting the equipment jackets.This gives me flow of 14 cu.m/hr in each line.The sum total of flow for all equipment which is
(flow in each line)*(no.of equipments). This total flow I have taken as discharge flow for the brine circulation pump.
Brine is ethylene glycol + water (50:50).
The procedure as explained by you is very correct which I know already.What I am doing is a sort of rating my existing chilling plant.
What I was expecting is that the data which is needed for designing compressor particularly compression data for different type of refrigerant, factors which decides optimum compression ratio,optimum compression Horse power.

Thanks
Trilok

[Art Montemayor]

Trilok:

Thanks for the quick response. And also thank you for understanding how I’m trying to help out. You titled the original post as “Chilling Plant Design” – so quite naturally, I responded to a design need and not to a “rating” need. This thread is going to be a long one and communications is what causes this.

A brine surge tank is certainly a need to fill in any brine system. However, it plays absolutely no role in determining the duty of the refrigeration evaporator. And I didn’t show it in my simplified PFD because of that. Now I know that you have an existing chiller. But you still haven’t identified the existing basic data:

The type of chiller unit: is it a reciprocating, screw, or centrifugal compressor? Condenser type: water or air cooled? Size & type of existing compressor? single stage? 2-stage? evaporator (brine cooler) required working pressure and temperature? Identification of refrigerant used? etc., etc. Condensing refrigerant temperature? What parameters do you want to vary – if any?

If you furnish the required basic data, I can easily set up the calculations to “rate” or size the refrigeration unit if that is what you need. I can furnish these in spreadsheet format, together with the PFD to identify the various streams and sizes just as I’ve furnished the prior PFD. I’ve done this many times in the past and never depend on a simulation program to “simulate” a simple refrigeration system. A spread sheet does it more accurately and simply. It is specific and customized for what you want it to do. You can do all of the design in one workbook very easily: all refrigerant flowrates; compressor capacity requirements; power requirements, utility requirements, line sizes, vessel sizes, heat exchanger sizing, etc. etc.

You say you were “expecting” a result. But you didn’t specifically ask for it. I can supply what I think you want, but you have to specifically ask for what it is you require. No problem here, but communication has to be established. For example, you mention an “optimum compression ratio” and you don’t state how many stages of compression you propose. If you have only one stage of compression, there is no “optimum” involved. The compressor’s compression ratio is fixed by the suction and discharge pressures and these, in turn, are fixed by the refrigerant’s vapor pressure at the evaporator and the condenser. If you can communicate with a simplified PFD of what you have, it makes for quick and accurate data communication. Everytime a word processor is employed like was done in your table with no units or calculations shown or references, it makes for a lot of confusion and lost effort/time.

Let me know.