{"id":80,"date":"2020-05-11T16:18:19","date_gmt":"2020-05-11T14:18:19","guid":{"rendered":"http:\/\/leroux.mobi\/blog\/?p=80"},"modified":"2020-05-19T22:04:30","modified_gmt":"2020-05-19T20:04:30","slug":"boiler-bits-7-the-case-for-oxygen-trim-control","status":"publish","type":"post","link":"https:\/\/leroux.mobi\/blog\/2020\/05\/11\/boiler-bits-7-the-case-for-oxygen-trim-control\/","title":{"rendered":"BOILER BITS 7: THE CASE FOR OXYGEN TRIM CONTROL"},"content":{"rendered":"\n

In Boiler Bits 5<\/a> and Boiler Bits 6<\/a> we looked into the significance of excess air as an absolute necessity for proper combustion, and its role as the major contributor to boiler energy loss.<\/p>\n\n\n\n

Imagine how convenient it will be to have an operational parameter which\nis representative of the percentage excess air of combustion, especially if\nthis parameter can be used to control excess air accurately towards maximizing\ncombustion efficiency. The good news is that such a parameter indeed exists and\nis being used in many combustion applications, not only with steam boiler\noperations, but also and in particular in the automotive industry.<\/p>\n\n\n\n

As we have mentioned previously excess air does not actively take part\nin the combustion process and it does not give up any of its oxygen to combine\nwith fuel atoms. It merely enters the furnace as ambient air and travels along\nthrough the system with the flue gas. But it leaves an oxygen footprint in the\nflue gas which tells us quite accurately the percentage excess air supplied to\nthe combustion system.<\/p>\n\n\n\n

Unknowingly many of us are using this oxygen footprint for excess air control on a daily basis. Getting behind the steering wheel of your fuel injected motor vehicle you are about to activate oxygen based combustion control which regulates the air and fuel mixture as part of the engine management system. A so called lambda sensor located in the exhaust gas stream continuously monitors the oxygen level of the combustion gas and by this means determines if the mixture is too lean (excessive excess air), or too rich (deficiency of excess air), or just right. It regulates the fuel injection system to continuously adjust the excess air (air-fuel ratio) to keep the engine performing at optimum levels of power, economy and emissions quality.<\/p>\n\n\n\n

Well, why not use this technology to enhance boiler performance? Oxygen trim control is widely used with oil, gas and pulverized coal boilers. But how effectively does it perform with chain grate stokers firing pea coal fuel? In my dealings with users of steam boilers I often encounter widely differing responses to oxygen trim control for pea coal firing, ranging from ignorance and apathy to total awe at the perceived superior efficiency of this technology.<\/p>\n\n\n\n

But first, back to the classroom. Let us assume that a combustion\nprocess firing pea coal requires 50% excess air for optimum combustion of the\nfuel. The stoichiometric air requirement for the relevant fuel feed is an\narbitrary 100 units and a further 50 units of excess air are added, giving us a\ntotal combustion air supply of 150 units. The 100 units of stoichiometric air\ngive up all of its oxygen in the combustion process and produce flue gas\nconsisting of CO2 and nitrogen. The 50 units of excess air on the other hand\npass through the system unchanged and exit the system containing 79% nitrogen\nand 21% oxygen on a volume basis. Thus on a volume basis the total flue gas\nmixture contains (50 units * 21%) = 10,5 units of oxygen. If we do a bit more\nnumber crunching (not shown here) we find that the 10,5 units of oxygen\nrepresent approximately 7% of the total volume of flue gas discharged through\nthe stack. Or to sum it all up: 7% oxygen in the flue gas is indicative of 50%\nexcess air. [Please note that this is a somewhat simplified approach, as the\neffects of hydrogen, moisture, sulphur, carbon monoxide, etc. are being\nignored. But do not stress, we are not so much into the chemistry as into the\nprinciples of combustion and its control, as well as of its practical\napplication.]<\/p>\n\n\n\n

This relationship between excess air and flue gas oxygen is a very handy\none to know. It means that if the oxygen content of the flue gas can be\nmeasured and controlled, the excess air percentage can also be controlled to\nprovide for optimized air-fuel ratios, provided of course one knows the optimum\nexcess air requirement of the fuel being burned.<\/p>\n\n\n\n

A well designed combustion control system will often incorporate a flue\ngas analyzer (oxygen sensor\/transducer) to accurately adjust (trim) the\ncombustion air supply in accordance with the fuel feed rate. Theoretically then\noxygen trim should enable one to operate the boiler at best efficiency under\nall load conditions.<\/p>\n\n\n\n

But is this a practical reality? Maybe it is easier said than done? In\nour next edition of Boiler Bits I will explore the Achilles heel of oxygen trim\ncontrol in greater detail.<\/p>\n\n\n\n

<\/p>\n\n\n\n

This post was compiled by Ren\u00e9 le Roux<\/strong> for Le Roux Combustion, all rights reserved. Do you want to know more about combustion control systems and 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 that our posts do not constitute professional advice and the comments, opinions and conclusions drawn from this post must be evaluated and implemented with discretion by our readers at their own risk.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

In Boiler Bits 5 and Boiler Bits 6 we looked into the significance of excess air as an absolute necessity for proper combustion, and its role as the major contributor to boiler energy loss. Imagine how convenient it will be to have an operational parameter which is representative of the percentage excess air of combustion, … <\/p>\n

Continue reading “BOILER BITS 7: THE CASE FOR OXYGEN TRIM CONTROL”<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","enabled":false},"version":2}},"categories":[1],"tags":[],"class_list":["post-80","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/leroux.mobi\/blog\/wp-json\/wp\/v2\/posts\/80"}],"collection":[{"href":"https:\/\/leroux.mobi\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/leroux.mobi\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/leroux.mobi\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/leroux.mobi\/blog\/wp-json\/wp\/v2\/comments?post=80"}],"version-history":[{"count":2,"href":"https:\/\/leroux.mobi\/blog\/wp-json\/wp\/v2\/posts\/80\/revisions"}],"predecessor-version":[{"id":134,"href":"https:\/\/leroux.mobi\/blog\/wp-json\/wp\/v2\/posts\/80\/revisions\/134"}],"wp:attachment":[{"href":"https:\/\/leroux.mobi\/blog\/wp-json\/wp\/v2\/media?parent=80"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/leroux.mobi\/blog\/wp-json\/wp\/v2\/categories?post=80"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/leroux.mobi\/blog\/wp-json\/wp\/v2\/tags?post=80"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}