Wednesday, January 13, 2010

Pressure Drop - Part 2

In the previouse article, I wrote about good and bad pressure drop and briefly explained about why we care about it from the beginning stage and while operating the plants or facilities. Here I'll further share about how can we utilize the pressure drop.

The pressure drop again as highlighted in previous article is actually due to the friction along the piping. In the meantime, it is not a significant losses relative to equipments. As we all aware there is allowable pressure drop for all the equipments such a way that pumps or compresssors can be sized properly to reach destination pressure. All the equipments need to be sized so that the pressure drop calculated is not beyond the allowable pressure drop. How does usually this pressure drop is affected or can affect the size/design of equipment? It is exactly same as happen to piping but than much larger pressure drop relative to friction losses. So, it is actually same principal where the friction losses inside the equipment as higher velocity will give higher losses. For new design, the equipment can be designed so that the calculated pressure drop lower than allowable. Unfortunately, what would happen if the equipment designed is giving higher pressure drop than allowable? How it can be rectified? Does it mean that the whole equipment need to be revamped?

Thursday, January 7, 2010

Pressure Drop

What do we know about pressure drop? What is all about? Where do we see this pressure drop? Is it a harm or benefit? How to differentiate between good and bad pressure drop? Why do we need pressure drop? Where do we need it? When do we need it? Why is that so important to consider the pressure drop? What is the difference between allowable and calculated pressure drop? How pressure drop can be manipulated in order to get the optimum performance of equipments?

As we all know pressure drop occur due to friction factor and it can't be zero but can be minimised as happen to fouling. Similarly the pressure drop can be minimised as much as possible by using very smooth material of pipe. However, this is not practicale to use very smooth material of pipe or equipment since it would not be feasible economically for large configuration of plants or processing facilities. So far while this para, people might think about the harm and benefit of pressure drop and obviously only the bad thing can be seen so far as it all talk about how to minimise it.

Here is the time to talk about good and bad pressure drop. The pressure drop again needs to be defined properly so that can differentiate between good and bad. These good and bad actually reflecting to the allowable and calculated pressure drop. We should know how to manipulate the pressure drop so that good pressure drop can be gained. Before the good and bad pressure drop can be explained further, the allowable and calculated pressure drop need to be understood correctly. In direct way, substraction of the allowable and calculated pressure drop dictating the pressure drop is a good or bad pressure drop. Do you have any idea on this? Usually if calculated pressure drop is higher than allowable pressure drop, then, the excess pressure drop is considered as bad pressure drop. This scenario is further explained later by referring to an example.

The allowable pressure drop usually is defined from overall allowable pressure drop of the system/unit/line. This system, unit, or line can be defined starting from discharge point of pump or compressor to the destination point. So, the allowable pressure drop can be defined as substraction of discharge pressure and destination pressure. Greater the deviation between these values, better the allowable pressure drop. However, it is not economical to design very huge margin of allowable pressure drop. So, have you got an idea how this allowable pressure drop can be considered as good pressure drop? Let us explore!