Monday, May 11, 2015

Lost olefin production and other happenings you don't want

In the April issue of Hydrocarbon Processing I found two articles about olefin production. The first was titled "Top seven causes for lost olefin production" written by Claire Cagnolatti from HSB Solomon Associates. HP claims it is an upgrade version of a present of a presentation at the AIChE T4 Topical Ethylene Producers 2014 Conference Spring National Meeting in New Orleans. A little googling reveals, that the material was also presented at the 2015 American Fuel & Petrochemical Manufacturers International Petrochemical Conference (IPC). The link to the latter version is here.

At the headline level the major area of lost - I would rather call it missed - olefin production is according to Cagnolatti: process problems; mechanical, electrical or instrumentation failures, utility supply problems and non-operational causes. Among the latter one finds "lack of product demand". Among utility supply problems one finds power failure and steam failure as well as other utilities. And among process problems "pyrolosis furnace decoking" is listed as a cause of downtime or lost production. I at this point start to wonder if the author has even been on an olefin unit for more than a brief visit?

The study of lost olefin production covers the period from 1999 to 2011. On the figure to the left the losses are shown relative to the losses in 2011, which is arbitrarily set to 100%. Based on this figure the authors states, that the losses have been on a general decline since 2011. I read the figure somewhat differently. 2001 is an unexplained outlier, and the losses have been on a increase until about 2009, when the high margins enjoyed by North American plants made lost production more costly. It should be noted, that the study is performed by HSB Solomon Associates every two years, and figure to the left is based just on data from North American plants.

The article also define a major event as one involving more than 5% of total lost production in that study year. Each study except the most recent contain 1, 2 or 3 such events. And no trend is evident in the number of major loss events.

Then the top seven causes are listed, as shown in the figure to the right. Unfortunately the causes listed in this figure are not in complete agreement with the causes listed in table 1. Pyrolysis furnace failure or availability is found to be responsible for the largest amount of lost production. That is really not surprising, when one know this include pyrolysis furnace decoking. I find is difficult to conclude anything from this figure, except that the contribution of control system and instrumentation failures are minor.

The author goes on with a detailed analysis of the top seven causes. Unfortunately the labelling again is not consistent with the used previously in the study, e.g. in the figure to the right or in Table 1. Neither is the factors which could e.g. cause cooling tower constraints analyzed. That is cooling tower constraint is considered a root cause.However, maybe the figure do indicate why the 2001 study showed higher losses that both the previous study in 1999 and the next in 2003. Changed decoke procedures?

The study also included a linear regression analysis showing that production loss was lower, when a higher percentage of maintenance was dedicated to preventive/predictive maintenance. Further work is however, needed on this regression before anything is concluded. However, there appear to be evidence, that plant suffering major loss events had more corrective or responsive maintenance and less preventive/predictive maintenance.

My conclusion is that one should be careful not seeing the trend, which one hope to see in some data-set, and that the relationship between preventive/predictive maintenance and negative events at a facility should be further explored - not just for olefin plants. Maybe here is another indirect indicator of the safety culture at
a facility.

The second article was titled "How Cr compounds discolor refractory brick walls of an ethylene cracking furnace" by M.Maity et.al from Saudi Basic Industries Corp. The picture on the left shows the refractory brick wall in the radient section of an ethylene cracking furnace at one of Sabic's petrochemical plant, and based on the article this is something you don't want to see in your plant. It turned out, that the pink material was a chromium compound, and its appearance was properly caused by the spontaneous formation of chromium oxide on the tubes at high temperatures followed by oxidative vaporization likely due to increase of the tube metal temperature to values above design. Unfortunately the article does not confirm, that the chromium came from the tube metal, but just stated that tube samples was analyzed for chromium concentration along the thickness to determine if the tubes were truly loosing chromium, and hence useful life. Unfortunately the answer is left hanging in the air.