For example, the Servicios Especiales Portuarios SA (SEPSA) facility is geographically a little different. \u201cWe have a large facility, and our location is prone to wind storms from the north, known as \u2018Los Nortes\u2019 in Spanish,\u201d explains director Andrew Gillespie. It\u2019s a particularly exposed, five hectare site: \u201cWhen we have operations running and the wind picks up, we need to relocate the equipment to accommodate that. It has to happen quickly and easily.\u201d<\/p>\n
SEPSA handles more than a million metric tons of bulk cargo per year, including shredded and structural scrap, pig iron, hot briquette iron, petcoke and fertiliser. As you can imagine, it is \u201csubject to close environmental scrutiny,\u201d says Mr Gillespie. \u201cThe Port Authority of Veracruz monitors our stockyard daily, and we also hire a third-party monitor to come several times a year to report their findings.\u201d<\/p>\n
It\u2019s a sensitive issue. So, SEPSA employs a high-volume air sampling system from Tisch Environmental to measure total suspended particulates and has also been using a DustBossfrom Dust Control Technology (DCT) since early 2011.<\/p>\n
Rick Felde of DCT explains that while this solution had its advantages there was the ongoing issue of frequent relocations to allow for changing wind conditions. So the answer was a customised, self contained and above all completely mobile solution. The operator sourced an old bulk tanker truck originally used for cement, \u201cwhich was useful because it had a large capacity\u201d says Mr Felde.<\/p>\n
The fitting meant mounting a diesel-driven generator on top of the tanker at one end with the dust suppression unit at the other: the water tank took up the main body of the unit, and other useful details were added, such as safety railings and an access ladder running up the side.<\/p>\n
The standard design atomised mist unit features a manifold of 30 brass nozzles that create millions of water droplets per minute with a range of 50-200 microns, giving a spread of both particle-size effectiveness and coverage area. The truck mounted unit then launches the droplets with a powerful 25 HP (18.6 KW) fan over a 60 metre range. However, the latest development is a machine with a range of 100 metres, engineered specifically to fight dust on large job sites, with a 60 HP motor and user-definable 359\u02da oscillation. This throws the mist more than 100 metres – so one machine could cover six football fields.<\/p>\n
The resulting rig is actually very versatile: SEPSA is primarily using it in storage areas to control dust during vessel unloading and material distribution to rail cars and trucks, along with occasional moves to the pier. One driver can relocate it virtually anywhere on the property to allow for shifting winds and changing jobsites, and, most importantly, do it quickly.<\/p>\n
The idea isn\u2019t limited to this application: another company, Pece of Mind Inc has put together a somewhat smaller version of the self-contained design that SEPSA came up with. This time the customer mounted the unit onto the back of the truck and ran it via a power take-off from the truck\u2019s engine.<\/p>\n
But what happens if you can\u2019t simply spray the cause of the dust?<\/b><\/p>\n
\u201cWe maintain an 80,000 sq foot warehouse used exclusively for storing wood pellets, which are a widely used biomass fuel in Europe,\u201d explained John Ramer, director of Terminal Services at the Panama City Port Authority. \u201cThe facility receives about 30,000 tonnes of pellets each month by rail car, creating stockpiles more than 100 feet wide at the base, with an enormous potential for dust,\u201d he said, adding that screens and other physical barriers \u201cjust weren\u2019t enough\u201d.<\/p>\n
The three front loaders have 10-yard buckets feeding a 600-foot conveyor. The pellets are then dumped off the conveyor and straight into the ships hold, creating a hug amount of dust.<\/p>\n
However, the difficulty is that you don\u2019t want to get the wood pellets wet. There are a number of reasons for this: pellets are usually compacted sawdust or other wastes from sawmills and often produced with a low moisture content (below 10%) specifically for very high combustion efficiency. This means pellets have an unusual ability to entrain water, and if they get soggy not only do they crumble but also they also lose their effectiveness.<\/p>\n
The answer was not to aim the mist directly into the hold, but to aim the water mist plume high, targeting the dust cloud hanging above the ship, an effective strategy since it minimised the pellets\u2019 contact with the water.<\/p>\n
This targeting of the plume is the obvious choice if you can\u2019t damp products too much, points out Stephen Larkin of Sealpump, which specialises in dry fog dust suppression systems.<\/p>\n
However, more control of the space is needed for fog to work. Mr Larkin explains that unlike the water misting applications the fogging should ideally take place inside a shrouded area to give the fog time to take effect on the particles before it gets dispersed by the wind. Realistically this is not always easy to manage, fog systems are not good for large open areas but these still have their uses at focused loading and unloading points.<\/p>\n
The fog itself is created by ultrasonic nozzles which produce extremely small water droplets in a range that runs from 2 to 10 microns, and so these are probably better at capturing dust below 15 microns in size. Further, dry fog dust suppression systems control airborne dust without wetting the product or site machinery, adding very little water. There is usually an accumulation of less than less than 1% additional moisture which makes it useful for concrete and coal dust transfer points on conveyors where the fog has the chance of being kept very localised.<\/p>\n
In contrast, misting systems do add a little more water to the environment, but as pointed out by Mr Felde, the mist can simply be targeted at dust plumes which means only a proportion of the droplets fall back onto the raw material.<\/p>\n
However, Mr Felde explains that the best way to entrap the particles \u201cis to tailor the droplets to the size of the dust particles\u201d, avoiding the slipstream effect that can occur when the two are mismatched. For example, a dust particle of 5 microns will tend to follow the air stream as it flows past a water droplet of 100 microns, slipping around it and avoiding interaction. The same phenomenon occurs when droplets are significantly smaller than the dust particles. But with a dust particle and a water droplet of similar sizes, the relative size of the air stream is more equal, facilitating a collision and subsequent agglomeration.<\/p>\n
However, Mr Larkin points out that smaller droplets do eventually bring down bigger particles, effectively by weight of numbers. And of course, in some cases low-velocity fog systems are going to be better if only because high-velocity sprays can add energy to the air and the dust particles, keeping them in suspension for longer if they are light enough.<\/p>\n
Which means, it really is horses for courses, or rather, droplets for particulates.<\/p>\n","protected":false},"excerpt":{"rendered":"
A port\u2019s airborne dust, you might assume, should be treated at the source and on the spot by an on-the-spot dust mitigation system. However, this easy answer isn\u2019t always practicable, writes Stevie Knight.<\/p>\n","protected":false},"author":8,"featured_media":2265,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[25],"tags":[],"sponsor":[],"class_list":["post-2264","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-energy-technology-greenport"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.portstrategy.com\/greenport-congress\/wp-json\/wp\/v2\/posts\/2264","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.portstrategy.com\/greenport-congress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.portstrategy.com\/greenport-congress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.portstrategy.com\/greenport-congress\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/www.portstrategy.com\/greenport-congress\/wp-json\/wp\/v2\/comments?post=2264"}],"version-history":[{"count":1,"href":"https:\/\/www.portstrategy.com\/greenport-congress\/wp-json\/wp\/v2\/posts\/2264\/revisions"}],"predecessor-version":[{"id":2266,"href":"https:\/\/www.portstrategy.com\/greenport-congress\/wp-json\/wp\/v2\/posts\/2264\/revisions\/2266"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.portstrategy.com\/greenport-congress\/wp-json\/wp\/v2\/media\/2265"}],"wp:attachment":[{"href":"https:\/\/www.portstrategy.com\/greenport-congress\/wp-json\/wp\/v2\/media?parent=2264"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.portstrategy.com\/greenport-congress\/wp-json\/wp\/v2\/categories?post=2264"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.portstrategy.com\/greenport-congress\/wp-json\/wp\/v2\/tags?post=2264"},{"taxonomy":"sponsor","embeddable":true,"href":"https:\/\/www.portstrategy.com\/greenport-congress\/wp-json\/wp\/v2\/sponsor?post=2264"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}