Energy gap
Question: The oil refinery near my home sports a constantly burning flame.
Other refineries around the world do the same. Why is this energy apparently
wasted and why can鈥檛 it be used as a power source?
Answer: In the early days of the oil industry, gas was a waste product and
was just flared off. Nowadays, however, gas is a valuable commodity and is
rarely thrown away. The flare your correspondent sees is only burning a very
small proportion of the gas produced in the refinery, and is there as a safety
measure.
The plant contains reaction vessels, pipes, compressors and other equipment,
all full of high-pressure gas. In an emergency this gas becomes a very real
danger and safety valves will be operated by emergency shutdown systems to
release it. But, just releasing the gas into the atmosphere would create as
great a danger as the system is trying to prevent, and so these valves are
connected to the flare.
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The flare is kept continuously burning so that, in an emergency, the released
gas would be ignited safely and burnt as it is released. Given this requirement,
the flame is kept as small as possible.
Dave Bush
Manchester
Answer: Flare stacks can prevent damage and death. If a large quantity of
highly flammable gas or liquid is released and forms a vapour cloud that
ignites, the consequences are severe. Notable examples of such failures occurred
in Flixborough in Lincolnshire in June 1974 and Pasadena, Texas, in October
1989. At Flixborough, a large, dense flammable cloud was formed when 60 tonnes
of cyclohexane were released accidentally. This cloud ignited and 29 people
died. In Texas, a polyethylene plant released a large quantity of ethylene and
isobutane when proper maintenance routines were not followed, killing 23 people
in the resulting explosion.
When the flares are put to use in an emergency, a considerable roar can be
heard and the flame size increases rapidly.
Robert Bacon
Old Amersham, Buckinghamshire
Cutting edge
Question: Is there any scale that measures the sharpness of cutting
implements. I鈥檇 rate a surgeon鈥檚 scalpel as 9.5 out of 10 but an ordinary table
knife as only 2.5. Is there a formal scale, and if not, why not?
Answer: The Cutlery and Allied Trades Research Association in Sheffield,
South Yorkshire, makes a sharp edge tester for this purpose, described by a
provisional Euronorm Standard outlined in the following reference: BS EN ISO
8442: 1999, part 5, 鈥淪pecification for sharpness and edge retention of
肠耻迟濒别谤测鈥�.
The device holds the blade to be tested with its edge facing vertically
upwards. The blade is then oscillated back and forth while a pack of specially
developed cards made of cellulose and quartz abrasive is lowered onto it under a
controlled load. The depth of the cut in the cards is the measure of sharpness.
By plotting the depth of card cut against the number of blade oscillations,
initial sharpness (known as Initial Cutting Performance or ICP) and wear rate
(called Total Card Cut, or TCC) can be defined (for more details see Surface
Engineering, vol 16, p 373).
D. R. McIntyre
Department of Materials Science
University of Cambridge
Staple issue
Question: Why do staplers have a rotating plate in the base so you can make
the staples fold inwards or outwards?
Outward-facing staples don鈥檛 hold the paper together as well, so what鈥檚 it
for?
Answer: The reason for outward-facing staples is that they are easier to
remove by hand. For a letter with a reply form, for example, which only has to
be held together temporarily, one can remove the form without tearing the page
or using a staple remover if an outward-facing staple has been used.
It鈥檚 a shame that many people are not aware of this alternative as it would
save torn fingernails and punctured fingers. Since most mass mailings now use
machines that force the staple ends together rather than outwards, we have to
put up with this. When there was human office labour, however, it was common to
receive mail with an outward staple.
Richard Turle
Gloucester, Ontario, Canada
Answer: Before staples were introduced around the beginning of the last
century pins were used to hold papers together. Although pins would stick to
other pages and surfaces鈥攏ot to mention office workers鈥攖hey were
easily removed, while the traditional staple was not. The outward-facing staple
eliminated this complaint.
Incidentally, pins for holding pages together had a slightly different design
from usual. They were filled under the head and had a pointed cap of metal,
giving the pin an almost diamond shape in vertical section.
Steven Reitci
Wauwatosa, Wisconsin
Answer: Certain professions (stockbrokers for instance) require items to be
pinned together as opposed to stapled. This makes it easier for the recipient to
separate the items quickly, such as cheques from application forms, when a large
number of items have to be handled. By rotating the base plate in the stapler it
is possible to mimic the use of a pin to hold items together.
Geoff Brown
Harlow, Essex
This week鈥檚 questions
Christmas cracker 1: During Christmas lunch, an argument began over whether a
water jug forming the container for a water filtration system, was made of glass
or plastic (or even some combination). When struck, the jug did not 鈥渞ing鈥� like
glass and some of its curves were suspiciously smooth. But in other respects the
jug felt exactly like glass. How could the argument be settled without smashing
the jug?
Christmas cracker 2: Then, during Christmas tea, another argument began. How
are the tiny edible silver balls that are used to decorate cakes made and what
produces the shiny, silver colour? Some of us thought the coating was aluminium,
but wouldn鈥檛 that be a health hazard?
Tammy Sand
Nottingham