July 26, 2010

ISO - Standard OR Business - 1

I am going to write a series on ISO system, its implementation practices, effectiveness, it's claims etc. in several parts in the form of a series. Anyone can put their frank opinion & comments on these write ups. We are not going to comment on ISO as organization but we are commenting on the systems, its effectiveness & industries which are implementing it.

Again this is not for criticism of any agency or organization; it is my experience sharing on actual implementation & loop holes in the system & its effective implementation.

I will show - How the basic purpose of this standard is defeated by standard itself - And my real experience no standards management expert or ISO expert who is responsible for its implementation is concerned about it - even after accepting these problems
resistively.

For reality purpose, we are referring the website quotes or matter from ‘ISO’ website.


1. Why Standards Matter?

This is the first question, the official website of ISO present to us, in a very nice & surely positive manner. It is soon justified that without ISO systems the product quality, incompatibility, cost and, safety are compromised.

One better paragraph on site says that - "ISO standards contribute to making the development, manufacturing and supply of products and services more efficient, safer and cleaner. They make trade between countries easier and fairer. They provide governments with a technical base for health, safety and environmental legislation. They aid in transferring technology to developing countries. ISO standards also serve to safeguard consumers, and users in general, of products and services - as well as to make their lives simpler." (Source : ISO Website)

Read on further claims - "When things go well - for example, when systems, machinery and devices work well and safely - then it is because they conform to standards. And the organization responsible for many thousands of the standards which benefit society worldwide is ISO." (Source : ISO Website)

Yes, Standards do matter & definitely help in making processes efficient, safer & cleaner as claimed but the difference do not lie in making a "voluminous standard", it lies in actual implementation & practice. The way ISO is implemented is totally useless as standard itself provides ways & means to enjoy bypasses to the spirit of the standard.

Therefore, it is neither helpful in making processes efficient as some or the other way is available to bypass the system nor safer or cleaner. ( How - You will see it through examples in the next parts of this series - Be patient).

There is no health, safety & environment improvement by implementing ISO....In fact, it is creating more problems to the environment - by using more papers - more documents - more consumption of power due to late sitting of ISO staff in organization to complete the time targets - late sitting for preparing for audits - many formats but only one line on one paper sheet - etc. etc. etc....

Even though I am not saying ISO system is bad - Mind it I am repeating - I say, ISO system needs further improvements in terms of its effectiveness.

The first problem I see is - to allow the manufacturer to go selectively. We will discuss this in next part.....



Disclaimer - This is a series of my personal views on ISO systems, its implementation, Effectiveness etc. They do not carry any legal issue related to my personal views under the human right of "Freedom of Speech".

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July 12, 2010

MVR - Use it for Higher Benefits


In my last post, I mentioned some background about mechanical vapor re-compression.

In this post I am going to illustrate some benefits out of MVR system.

In general they must be seen as energy saving schemes in the current scenario of high energy costs in most of the processes. The need to recover or re-utilize energy is essential in thermal separation processes such as evaporations, distillation etc.

Following are the general options available in the industry out of which MVR is the most unutilized or neglected one while being the most efficient one.

1. Multi Effect evaporation (MEE)
2. Vapor re-compression
a. Thermal recompression
b. Mechanical recompression



I am not covering other options as they are well known as my focus here is to mainly emphasize on the benefits of MVR. However, for comparison purpose we will start with MEE only.

MEE
In a multi effect evaporation plant, the vapors produced in the first effect are utilized as the heating medium of the second effect and so on. This effectively reduces steam consumption in proportion to the number of effects. Ideally unit mass of vapor on condensation can evaporate unit mass of liquid. The vapors generated at the first effect are condensed in the second stage to further evaporate the liquid from the second stage and so on. A temperature gradient of about 7-10°C is maintained between stages for maximum efficiency.

So a triple effect evaporator would consume only 35-36% of the energy in comparison to a single effect system. Thus for each kg of steam input to first effect we can theoretically produce 3 kg of evaporation, practically it would be as below because of efficiency of evaporation in the subsequent systems. So let us work on some nos.

The efficiency of 95% is assumed in all evaporation systems through out this comparison

Feed to first effect (say) – 1 Kg steam
The evaporation from first effect – 0.95 Kg steam
The evaporation from second effect – 0.90 Kg steam (i.e. 0.95 x 0.95)
The evaporation from third effect – 0.86 Kg steam (i.e. 0.90 x 0.95)

So total evaporation possible in a 3 stage MEE is = 0.95+0.90+0.86 = 2.71

This is generally the overall economy ratio of a 3stage MEE system. This means for every kg of live steam fed to the system you can remove 2.71 kg of water from the MEE system. Thus, the so called COP is 2.71.

Thermal recompression
Now let us see thermal recompression system which is nothing but an ejector system which boosts the pressure of first effect evaporation by using higher pressure steam so that it can be utilized in the next effect. The major difference is that it requires high pressure steam to elevate the pressure of evaporated steam and may or may not require pressure gradient in the system which is essential in MEE.

Initially, heating steam is used to initialize evaporation. The vapors evaporated are compressed to higher pressure and temperature by steam jet ejector, condensed back for heat recovery and the residual vapors are taken to second stage for condensation / heat recovery. The amount of surplus energy contained in the residual vapor corresponds to the amount of energy supplied for steam jet ejector operation. This is taken as additional heat input / work done for recovery of large heat content of the evaporated vapors

So by theory practically the economy ratio is 1 for thermal compression system as whatever energy we put into the system in terms of motive steam is recovered back in the condenser of the next stage.


MVR
So now it’s a turn of MVR system. The process is that the initial vaporization is done using steam or electrical heater to initiate the process & then system may balance itself if you run only one stage of evaporation (by inherent nature of the process & economy ratio you do not need more than one stage practically unless there is a huge requirement or some mechanical issue is involved). So let us now see the calculations.

Every kg of steam initiated from the system is already having its latent heat. Let us assume that the process is near atmospheric condition. So the latent heat is ~2257 KJ/Kg at 100 C & 1 bar.

Now this steam is taken by the compressor & compressed to bit higher pressure. The energy required for compression is given as electrical energy which is increased by the efficiency terms over & above the theoretical requirement. This compression energy depends on pressure ratio. Generally MVR are currently designed to a pressure ratio limit of 1.5. So if the compressor is increasing the pressure to say 1.5 bar then the work done by compressor is

W = (P2 – P1) x Vs x 100

W = specific work done = KJ/Kg
P2 = final pressure = 1.5 bar
P1 = initial pressure = 1.0 bar
Vs = specific volume of steam = 1.67 M3/Kg

So the energy required is

W = (1.5 -1.0) x 100 x 1.67 = 83.5 KJ/Kg

Now let us assume overall efficiency of compression process including electrical, transmission efficiencies is 60%. Then total actual energy requirement is

W = 83.5/0.6 = 139 KJ/Kg

This means by putting an energy of 139 KJ/Kg, we can recover the latent heat of 2257 KJ/Kg out of steam. Therefore by definition of COP of the process, it is

COP = 2257 / 139 = 16.2

This means that one stage of MVR is equal to 16 stages of MEE in terms of energy efficiency. This also means that energy equal to one kg of steam put into an MVR will or can evaporate 16 Kg of steam from the system.

Benefits
Now in terms of cost of energy, theoretically the power cost is double than steam cost. So effectively the ratio will be 16.2/2 = 8. Thus, effectively the operation cost can be reduced by 8 times in comparison to MEE or any other option.

Following are the other advantages

  1. Low specific energy consumption i.e. energy consumed per kg of product.

  2. Unmatched Higher Performance co-efficient i.e. the overall economy of the operation.

  3. Gentle evaporation of the product due to low temperature differences and hence useful for temperature sensitive operation. In fact it is never a problem for any material because it operates only at very low delta T.

  4. No load or reduced load on cooling towers as there is no CW condenser in the system.

  5. Simplicity of process, operation & maintenance.












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