8 replies to this topic

[Art Montemayor]

Ananya:

You probably are not getting any response to what is a probing and interesting real-life type of problem because your schematic flow diagram isn’t that easy to grasp. I believe I have a better version and I am attaching it to show how a flow can be depicted in a simpler fashion, making it easier to understand and grasp the scope of what is being done. Note that all flows originate from the left and exit to the right of the sketch. Also note that utility fluids – such as your compressors’ cooling water - are kept out because they play no important part in the over-all process. It is important to show all fluids that enter the over-all process. You failed to note where the air is introduced. It is important to note that you are using atmospheric air to introduce into the process as a pneumatic medium.

Note how easy it is to sketch out a flow diagram in Excel. Engineers should always use a spreadsheet to calculate and to sketch out their ideas. Never employ a Word Processor (like Word for Windows). Word processors are for writers and poets; spreadsheets are for engineers.

You are introducing water moisture into your jet mill (and consequently into your Benomyl product via the compressed air you are using to pneumatically carry the product out. That is why it is so important to note ALL the entering streams as well as all the exiting streams on a PFD (process flow diagram). You should also sketch out the TYPE of air compressor you are using. In my sketch I am assuming you are using a reciprocating type, but it could be a screw type or centrifugal type. Reciprocating and screw types can introduce oil as a serious contaminant and that is why you should indicate the type of compressor. All air compressors employing atmospheric air as a source will produce an air stream at higher pressures that is saturated with water vapor. The water originates from the humidity that is inherently in the atmospheric air. If you are serious about producing a high quality of Benomyl product then the only solution is to dehydrate (“dry”) your compressed air stream. I would employ an adsorption type of dryer – depending on the flow rate and pressure levels of the air employed. I am assuming you are using an air flow in the range of 100 to 200 Scfm at approximately 100 psig. These are basic data that you don’t mention, so I’m not in a position to make further comments.

I hope this information helps you out and points out where your process is flawed and needs improvement to produce a quality product.
 Moisture_Content_in_Product.xls   33.5KB   113 downloads

[Art Montemayor]

Ananya:

Please refer to the attached revised Workbook and note the detailed flow diagram I’ve sketched out for you.

Now that I know the details of your air feed, I highly recommend you install an adsorption dryer downstream of your air compressors. This type of dryer will dry your pneumatic air down to parts per million (vol.) of water moisture in the pneumatic air. I have used this type of dryer in conjunction with reciprocating compressors and have always had 100% success. I started out by installing purchased units from manufacturers and later designed, installed, and operated my own units in the field. I’ve used them on air, CO₂, Hydrogen, Nitrogen, Nitrous Oxide, Methane, and other gases.

You are wrong to expect a large pressure drop from such a dryer. I would estimate that I can design such a dryer to consume only 1 to 5 psig of pressure – depending on the type of regeneration cycle chosen. You will never notice the pressure drop in your process particularly with the type of compressors being used. This dryer will also remove any oil contamination that always is present in oil-lubricated reciprocating compressors. This is a very important additional feature when you are producing high-purity, small volume of fine chemicals as I suspect you are doing.

The adsorption type of dryer can be manually operated or fully instrumented for automatic service and it can be designed on various types of regeneration and cycle methods – all depending on your needs and availability of waste heat or other sources of heat, like steam. You can find out about this type of drying system in the InterNet or in text books. Some adsorbents produce fine dust with continual, cyclic use and it is always wise to install an efficient filter downstream of the dryer in order to capture this dust and not contaminate the ultimate use of the air.

I hope this helps you out.

(Note: I've made a revision on the air dryer PFD to show the compressor aftercooler and water separator that is needed prior to the dryer itself.)
 Moisture_Content_in_Product.xls   56.5KB   109 downloads

[Art Montemayor]

If you follow the recommendations I've posted on the application of an adsorption air dryer, you won't have any problem with water vapor condensing within the system due to free expansion cooling (Joule-Thomson Effect). Since there practically will be no water moisture in the air due to the ultra-high removal of water by the dryer, you have no need to be concerned with liquid water formation. This is precisely the main reason for my continuing to make my recommendation. The water can only be introduced by the atmospheric air; remove the water (using an adsorption dryer), and the results will be:

1. No water or oil contamination on the End Product;
2. High Product quality;
3. No process problems due to water formation;
4. Continuous and easy operations of the process.

The best way to "control" the moisture is to eradicate or remove it.