We recently had the privilege to\nsupply and install a rather advanced boiler control system for a brewery in a\nneighbouring country. The system contained all the bells and whistles normally\nassociated with a system of this nature and we set aside sufficient time for\ntraining of both the operating and management staff, which took place in three\nseparate sessions. <\/p>\n\n\n\n
At each session there was only one question\nduring Q&A time \u2013 where can we see the daily coal consumption? I almost got\nthe impression that we misinterpreted the client\u2019s requirements for a control\nsystem \u2013 in reality they only needed an accurate coal counter, which we could\nhave provided at a fraction of the cost of a full blown control system. <\/p>\n\n\n\n
It wasn\u2019t long before we discovered the somewhat overly interest in a coal counter – the performance of the steam plant was measured by one indicator only, namely coal usage per unit of liquor produced. Although it seems like a logical measure of performance, it would only make sense if the coal characteristics remained consistent for all time. Which brings me to the way one should look at coal and indicators based on its usage. <\/p>\n\n\n\n
For many a person involved with steam\nproduction coal is a generic term for a black solid fossil fuel delivered in\ngravel size chunks, of which the quality is determined by the grade: A-grade\nbeing the best and D-grade being rather poor. To worsen matters coal\nprocurement is often made the responsibility of the Buyer \u2013 a person who in all\nprobability has never seen a boiler in operation. And his only perceived\ncontribution is buying A-grade coal (which it often is not when delivered!) at\nthe lowest cost. <\/p>\n\n\n\n
Fact is that coal is merely the carrier of the\nenergy required to produce steam. The energy content (referred to as calorific\nvalue or CV) is released during combustion of the coal. Now the peculiar thing\nabout coal is that there are numerous characteristics determining its ability\nthe convert it\u2019s CV into usable energy. Even coal of various origins with\nsimilar CV may render different efficiencies when fired in the same boiler. (I\nwill address significant coal characteristics in a future publication, so\nplease accept as fact what is written here for now). <\/p>\n\n\n\n
By implication then a kg of A-grade coal from various sources will not necessarily render the same quantity of steam. It thus becomes clear that the value added by coal is not so much in the CV of coal burned, as in the efficiency with which the CV can be converted into useful <\/strong>energy. In this respect the cost per unit of useful energy released by coal plays a much bigger role in the productivity equation than anything else. This then also implies that D-grade coal (at lower price per ton) can be more productive than A-grade coal (at higher cost per ton).<\/p>\n\n\n\n Time for an example. <\/strong><\/p>\n\n\n\n Since the quantity of energy required to\nproduce a unit of steam (and product) remains the same in all instances, the\ncost per ton of steam is proportional to the cost per GJ of useful fuel energy.\nIf we assume that one GJ of energy produces 0,4 tons of steam under specific\noperating conditions, then the fuel cost contribution to the cost per ton of\nsteam produced is as follows:<\/p>\n\n\n\n Those whose performance is measured against the steam-coal ratio indicator will probably jump at the opportunity to get hold of Coal X, ignoring the fact that it is not really such a great contributor to productivity as Coal Y would be. Furthermore, if a batch of Coal Y lands on site, the steam-coal ratio will drop significantly, despite the fact that productivity has improved. <\/p>\n\n\n\n My personal opinion of the matter is that the\nonly sensible and accurate indicator for the efficiency of steam generation is\nthe contribution of the cost of coal to the cost per unit of steam. And this\nnumber is really easy to calculate \u2013 the only data required is total steam (or\neven feed water) used, total coal consumed and the cost of coal delivered on\nsite. <\/p>\n\n\n\n The great advantage of this indicator is that\nit can be put to good use to optimize combustion conditions. By changing coal\nsuppliers (coal characteristics), excess air, steam pressure control set point,\netc. one may be able to find a combination of coal and combustion settings\nwhich yield the lowest cost per unit of steam. <\/p>\n\n\n\n Please note that the above example does not\nconsider the fouling tendencies of coal, which may contribute towards more\nregular cleaning of boiler tubes. <\/p>\n\n\n\n This post was compiled by\u00a0Ren\u00e9 le Roux<\/strong>\u00a0for Le Roux Combustion, all rights reserved. Do you want to know more about efficiency of combustion or combustion optimization? Please contact us for your professional boiler automation, steam system efficiency and coal characterization needs.<\/em><\/p>\n\n\n\n Kindly note\nthat our posts do not constitute professional advice and the comments, opinions\nand conclusions drawn from this post must be evaluated and implemented with\ndiscretion by our readers at their own risk.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":" We recently had the privilege to supply and install a rather advanced boiler control system for a brewery in a neighbouring country. The system contained all the bells and whistles normally associated with a system of this nature and we set aside sufficient time for training of both the operating and management staff, which took … <\/p>\n