Safety Valve Noise

7/23/2019 Safety Valve Noise

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SAFETY VALVE NOISESafety valve noise; limits, reduction and control

By M. D. G. Randall,

Foster Wheeler Energy Ltd. Reading,

Berkshire, UK.

First a little pilosopy

As a contractor's engineer, one ants to ha!e a "odel or other "ethod o# sol$tion in %lace &e#ore one

"eets a ca$se #or its $se. $rely to ha!e (no a!aila&le "odel( shos a&sence o# %rior tho$ght. o"e"odels ill sho lack o# tho$ght. As e)a"%les e "ight think o#* a "odel inconsistent ith knon #acts orco""on sense+ no data to s$&stantiate the "aths+ %redictions inconsistent ith the data. We ill allacce%t that a si"%le or &asic "odel is &etter than no "odel at all, &eca$se, as in#or"ation is gathered, thee)tra descri%tions and data can &e $sed to i"%ro!e or change the "odel.n the #olloing disc$ssion the reader ill #ind e)a"%les o# a si"%le "odel, old in#or"ation, and iss$es thatare not ell de#ined, &$t ith hich it is s$ggested he ork at the %resent ti"e. -o a%ology is "ade #orthis. he iss$e o# noise #ro" sa#ety !al!es does not a%%ear to &e ell co!ered in the general literat$re and&y "aking re#erence to iss$es here there is $ncertainty, the a$thor ho%es that others "ay &e enco$ragedto add de#inition or associate n$"erical res$lts to the".

What is a sa#ety !al!e/ 0o o#ten, long and lo$d is its noise/he sa#ety !al!e is a de!ice to a!oid a dangero$s &$ild1$% o# %ress$re ithin a syste" that it is designedto %rotect. 2ne sho$ld ne!er #orget that any redesign o# the 34 syste" "$st not decrease the sa#ety o#

the %rotected syste". A sa#ety !al!e is nor"ally $sed ith co"%ressi&le #l$ids, hereas a relie# !al!e is%ri"arily $sed ith inco"%ressi&le #l$ids 5see the introd$ction to Re# 67. he sa#ety !al!e is generallyknon as a 34 and "ay release the %rocess #l$id directly to the at"os%here !ia a short st$& %i%e, orrelease the %rocess #l$id !ia a %i%e to a #lare, or so"e other e8$i%"ent. hese ill &e called (o%en !ent(and (closed( 34 syste"s, res%ecti!ely. A 34 is act$ated &y $%strea" %ress$re and is characterised &yhat is descri&ed as a (%o%( action $%on o%ening. t is i"%ortant to recognise that one sho$ld not e)%ect agentle release o# gas %ro%ortional to !al!e li#t.he noise #ro" "a9or 34s can &e e)%ected to &e in the region o# 6:; 16


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can &e e)%ected to &e in the region o# 6;; to 6=: dB5A7 o$nd Le!el 5L7. he 66: dB5A7 li"it in A3 EA;6 can &e considered ty%ical 5see %ages 6?,6< o# Re# =7. he so$nd le!el is to &e "eas$red or%redicted at the orker location 5or here he is e)%ected to &e7, i.e. at gro$nd le!el, and on %lat#or"s,ladders, and stairs. o"eti"es this can &e !ery close to a 34 or its o%en !ent.34 noise is radiated #ro" the associated %i%ing and e8$i%"ent as ell as the all o# the 34. With o%en!ent syste"s the "a9ority o# the noise e)its !ia the o%en !ent at the end o# a st$& %i%e. n addition to this,noise "ay &e generated d$e to the "i)ing o# the high !elocity gas ith the s$rro$nding air. 34s ith st$&

%i%es to at"os%here "ight occ$r ith stea", air, or nitrogen, &$t rarely ith hydrocar&ons.

What reg$lations and standards a%%ly to 34s and their noise/-ot all co$ntries and standards organisations re8$ire that the sa#ety !al!e &e treated as a so$rce o# so$ndhich has to &e li"ited.As an e)a"%le o# hat "ight later &e seen as an enlightened standards organisation, e can look at-2R2K and its !ie that noise #ro" 34s sho$ld not &e considered d$ring design. 5see ection ?.:.= o#Re# >7 @he noise li"its shall not a%%ly to design e"ergency conditions e.g. near sa#ety 111 !al!es,#ire%$"%s or o$tdoor areas d$ring #$ll e"ergency #laring, etc.n the original %a%er a list o# UK legislati!e instr$"ents as %resented so that the reader "ight re!iethe" and anser the 8$estion, ( Does this doc$"ent a%%ly to "y syste" and its 34s/ hat list related tonoise and "ore general sa#ety "atters. -o s$ch list is %resented here. t ill &e #or the indi!id$al designer,here!er he is in the orld, and here!er the %ress$rised syste" is &eing installed*

6. to #ind the a%%ro%riate codes and standards,

=. to decide ho they are to &e co"%lied ith.

0ere are to doc$"ents hich incl$de noise li"its that see" a%%ro%riate #or any re!ie o# 34 noise.

A3 Medical Research Re%ort EA ;6. 5Re# =7his doc$"ent dates #ro" 6. t descri&es the sit$ation $nder disc$ssion today. t set a li"it o# 66:dB5A7 to steady so$nd, and 6C; dB5%eak7 to i"%$lsi!e noise. hese ere &ased on the data in the U.20A 6; " distant #ro"a 34 !ent o# so$nd %oer le!el 53WL7 is calc$lated &y $se o# the e8$ation,

o$nd %oer le!el is calc$lated &y $se o# the e8$ation*


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he M=ter" is the kinetic %oer o# the choked #lo thro$gh the !al!e, and the sy"&ol h is #or theaco$stic e##iciency associated ith the trans#or"ation o# so"e o# the kinetic %oer to so$nd %oer. M isthe "ass #lo rate. is the s%eed o# so$nd in the choked gas th$s, =H kIRI 5MW7. Franken shos thath ranges &eteen a&o$t 6;1:to 6;1=.

With the a&o!e to e8$ations the Franken disc$ssion leads to an e8$ation #or the 3L at >; "*

3L>;H 6;ILog@M=I J 7

Franken %ro!ides a gra%h o# h !s. 3ress$re Ratio.

he A3 #or"$lation #or 3L at >; " is si"ilar*

3L>;H 6;ILog@M= J 56;ILog@ J , can &e $sed #or%ress$re ratios a&o!e three, a #or"$la res$lts #or the so$nd %ress$re le!el at >; " hich is*

3L>;H 6;ILog@M

=

J :: 5:7

2ther "ethods that are $sed #or calc$lating the so$nd %oer le!el o# 34's can &e #o$nd in the technicalliterat$re. We had one %ro9ect at Foster Wheeler Energy here there as a %roli#eration o# 3WL %rediction"ethods and e #o$nd it e)%edient to initiate a la&elling syste". n this syste" the initials o# a "ethodsa$thors ere ritten a#ter the sy"&ol 3WL to indicate the so$rce o# the calc$lation. -ote that no one"ethod a%%ears to ha!e &een ado%ted &y the (!al!e ind$stry( and that no international standard e)itssolely #or the calc$lation o# 34 noise.

he reader "ay ish to calc$late an e)a"%le, so a rele!ant data set is gi!en here,

Mass #lo rate M C; kg s16

tea" MW 6

Ratio o# s%eci#ic heats k 6.=?Uni!ersal gas constant R .>I 6;> K165kgMole716


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e"%erat$re >;; J= K

3ress$re ratio 3R ?6 * 6

A %rediction "ethod #or noise at orker %ositions d$e to 34 !ents as re8$ired, and in the a&sence o# anacknoledged and acce%ted "ethod, the #olloing si"%le one as de!elo%ed to #ind the so$nd le!el at anangle and distance #ro" a %i%e !ent. onsideration is gi!en here to the case o# an (o%en !ent( rather than

a (closed( syste" as it ill &e seen to re%resent the "ost onero$s case.

t is reasona&le to s$%%ose that the noise at the orker %ositions close to an o%en !ent 34 ill &e a#$nction o#*!al!e &ody and %i%e radiation 5the"sel!es #$nctions o# #re8$ency7radiation #ro" !ents hich are directly to at"os%here 5 a #$nction o# #re8$ency7the distance to the nearest ( orker %osition(any directi!ity associated ith the ratio o#, a!e length o# so$nd to !ent dia"eter 5 the gas "ay &e cold orhot and %ossi&ly a&o$t "ach ;.:7.

Ass$"%tions ere+

6

.

he A3 :=6 calc$lation %ro!ided a dB5Lin7 !al$e that co$ld &e a%%ro)i"ated to the sa"e !al$e in

dB5A7=.

Directi!ity #actors #or the st$& %i%e's !ent co$ld &e #o$nd and $sed.

>.

A %eak #re8$ency o# noise co$ld &e selected so as to act as a g$ide to the directi!ity #actor.

C.

Red$ction o# noise ith increase o# distance o$ld #ollo the in!erse s8$are la.

A si"%li#ied set o# directi!ity c$r!es as $sed #or the initial trial calc$lations ith this "ethod. hey%ro!ided the increase or decrease o# so$nd ith angle and ere &ased on data in 4R co$rse notes5 ee ha%ter o# Re# 7 hich as itsel# &ased on BB- data #ro" 6:= and 4D >> data o# 6>. hisdirecti!ity data is not gi!en in 4D >> o# $ly 6?. his data as red$ced to a directi!ity ta&le a#ter theselection o# a %eak #re8$ency to act as a g$ide to the directi!ity #actor. ee Fig = #or an e)a"%le &ased on

6;;; 0.

Fig. Figure 2. Assumeddirectivity (in dB) at 1000 Hz.

nitially, there as a lot a ork in!ol!ed in gathering the data on the %ositions o# the %lat#or"s ladders andstairs, and the %ositions o# the closest 34 !ents, &$t no, ith the hel% o# Foster Wheeler ntergra%h >D3D it is a "$ch 8$icker %rocess.An e)a"%le o# a 34 noise s%readsheet is gi!en in Fig >. his s%readsheet shos the (sa#e distance( athich a orker "ight stand. (a#e distance( is de#ined as the distance at hich the so$nd #ro" the 34has red$ced to the sa#e le!el. he sa#e le!el ill &e the le!el set &y the oner, &$t is ty%ically 6;; to 6=:dB5A7 L as as noted in ection >. he sa#e distances #ro" the o%en !ent and #ro" the %i%e are di##erent

&eca$se the r$les #or noise atten$ation ith distance #ro" these ty%es o# so$rces are di##erent. Weass$"e that the so$nd #ro" the !ent #alls o## at a rate in!ersely %ro%ortional to the s8$are o# distance #ro"the !ent. We ass$"e that the so$nd #ro" the %i%e #alls o## at a rate in!ersely %ro%ortional to the distance


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#ro" the %i%e. At the #oot o# the s%readsheet there is a arning o# the res$lts o&tained #ro" these si"%leass$"%tions. he data shon as entered is not (real( &$t is realistic and a (sa#e distance( can &e seen #or&oth !ent and %i%e radiated noise at a range o# so$nd %oer le!els and so$nd %ress$re le!els at 6"distance #ro" &oth the !ent and the %i%e all. he ta&le has &een si"%li#ied to the &are essentials. -odirecti!ity corrections are "ade in this e)a"%le and the e##ect o# %i%e all trans"ission loss isde"onstrated only &y a constant di##erence o# =: dB &eteen col$"ns ? and . 0o do e de"onstrate &y calc$lation that the li"its ha!e &een co"%lied ith/

C. o"e organisations a&sol!e 34s #ro" co"%liance ith noise restrictions in e"ergencyconditions.

:. t o$ld a%%ear that so"e 34 !endors ha!e yet to %ro!ide noise data #or their ranges o#sa#ety !al!es.

?. ontractors "ay ha!e $nderstood their o&ligations &$t #ind it di##ic$lt to %ro!ide acc$ratein#or"ation on the L or 3L to &e "eas$red at selected orker %ositions.

Re#erences


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6. A3 R3 :=;. iing, selection and installation o# %ress$re relie!ing de!ices in re#ineries.3t 6. iing and selection 5March 6>73t =. nstallation 5Dece"&er 6C7=. G$idelines on noise. Medical Research Re%ort EA ;6. A3 6>. Design %rinci%les* Working en!iron"ent. -2R2K tandard 1D31;;= Re! 6, Dec. 6C 532 Bo) :C


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:. in9ection o# ater to cool the %rocess #l$id, say air or stea"+

?. ater c$rtains to act as a &arrier to so$nd+

Safety Valve Noise

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