tratamento de Água e problemas ocasionados

8/3/2019 Tratamento de gua e problemas ocasionados

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FLUDOS TRMICOSAr quente, gua quente, gua sobreaquecida, vaporsaturado, vapor sobreaquecido e leo trmico, mercrio,misturas de sais orgnicos, etc.Aquecimento por aco de uma energia exterior:radiao solar, combusto, electricidade, nuclear,geotrmica.Fluidos trmicos transportadores de energia trmica emecnica


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Quais os critrios que presidemescolha de um fludo trmico?

Temperatura, presso e potncia exigidas,estabilidade trmica, capacidade trmica,viscosidade, aco sobre o meio ambiente

(toxicidade, irritao da pele, odor forte), risco deincndio e exploso, boa compatibilidade commetais e ligas, normalmente empregues em

instalaes, preo.


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Requisitos exigidos a umfluido trmicoBoa estabilidade trmica

No atacar o material onde circulaPonto de congelao baixoBaixa presso de vapor

Viscosidade baixaAlta capacidade trmicaAlta condutibilidade trmica

Barato e de fcil obtenoNo ser txicoNo irritar a pele

No ter odor forte


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Fluidos trmicos

mais comunsArguaVaporleo trmico


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VantagensNo txico nem inflamvelBoa estabilidade trmicaReposio muito fcilBaixo custo

Dispensa a presena de fogueiro

DesvantagensBaixo coef. trans. calorExige ventilador para circulaoExige depsito de expanso casocontrrio provoca aumento dapresso

AR


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Vantagens1. Boa regulao da temperatura2. Fcil reposio3. No txico nem inflamvel4. Boa estabilidade trmica5. Elevado coeficiente de

transferncia de calor6. Causa menos problemas de

corroso que o vapor

Desvantagens1. Presso de vapor elevada2. Causa mais problemas de

corroso que o leo trmico3. Necessita de depsito de

expanso4. Necessita de bomba de circ.5. Exige tratamento qumico6. Exige presena de fogueiro

7. Exige presso p/ temp. altas

GUA


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Vantagens1. Elevado coef. trans. Calor2. Boa estabilidade trmica3. No inflamvel nem txico

4. Reposio barata5. No requer bomba de circ6. No exige desito

de.Expanso7. Boa relao

presso/temperatura

Desvantagens1. Mais corrosivo que a gua2. Exige tratamento qumico3. Exige altas presses para altas

4. temperaturas5. Exige sist. de recuperao decondensados para diminuir perdastrmicas.6. Perdas trmicas elevadas7. Exige presena de fogueiro8. Exige exames peridicos caldeira

Vapor


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Vantagens1. Baixa presso de vapor2. No causa problemas de corroso3. Dispensa a presena de fogueiro

Desvantagens1. Baixo coef. de trans. calor2. inflamvel3. Viscosidade e densidade variam

significativamente com a

temperatura4. Exige bomba de circulao5. Exige depsito de expanso6. Coloca problema de flexibilidade da

tubagem para

T alto7. caro

leo trmico


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A caldeira aquece o fluido, aps passagem por uma bomba centrifuga, queposteriormente distribuido pelos locais e equipamentos utilizadores de calor.

O fluido no sofre mudana de fase, estando sempre no estado liquido,e ainstalao opera a presses que variam entre 1,5 e 3,0 kg/cm2.(1 kg/cm2 = 0.9810 BAR )

H no entanto quem trabalhe com presses sada da bomba da ordem das 5

a 6 bar, permitindo vencer uma maior perda de carga na rede. A perda decarga uma das consequncias da necessidade de aumentar as velocidadesdo escoamento para melhorar a transferncia de calor e ganhar tempo nosprocessos de fabrico.

As modernas caldeiras de fluido trmico so compactas, simples, robustas,automticas, e protegidas por aparelhagem de controlo, podendo atingirrendimentos trmicos iguais aos da maioria das caldeiras de vapor.

Uma caldeira bem projectada pode atingir um rendimento de combusto de

cerca de 85%, e o rendimento trmico global, entrando em linha de conta comas perdas de calor por irradiao na caldeira, encanamentos, permutador decalor e aparelhagem auxiliar pode com frequncia atingir valores da ordem de75 %, num sistema equivalente a vapor se atingiro valores mximos de 55 a65 %.Quanto manuteno, ela incide normalmente no queimador e na bomba de


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Caractersticas dos fluidos trmicos

so geralmente derivados do petrleo com bases de naturezaparafnica ou naftnica. cuidadosamente selecionadas, uma vezque os leos vo ser submetidos a condies de trabalho muitoseveras, nomeadamente temperaturas de trabalho muito

elevadas durante longos periodos de tempo.Tipos de fluidos orgnicos trmicos so:hidrocarbonetos sintticos e teres poliaromticos - T < 400 C

esteres orgnicos - T < 232 Cglicis polialquilnicos - T < 260 Cesteres de silicatos - T < 350 C

Propriedades Fludos TrmicosEstabilidade oxidao, estabilidade trmica,Elevado ponto de ebulio,Boa condutibilidade trmica,

Baixa viscosidade a baixasTemperaturasInrcia qumica.


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A oxidao

Ocorre por contacto do leo com o ar, e para umatemperatura e actividade cataltica constante, a taxa de

oxidao aumenta se se borbulhar ar atravs dotermofluido.Os depsitos de particulas formam uma espcie de

lodo que endurece progressivamente nas superfcies atemperatura mais elevadas, transformando-sedepoisem depsitos carbonosos.

Num sistema de transmisso de calor por termofluido afuncionar em circuito fechado a oxidao poucointensa.


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A estabilidade trmica dos termofluidos de

baixa e mdia viscosidade normalmente muito boa;alterao da estrutura qumica provocada por aquecimento (cracking ou pirlise) noocorre para temperaturas inferiores aos 300 - 320 C , mas aumenta acentuadamentequando a temperatura ultrapassa os 350 C.

Para os leos de elevada viscosidade a pirlise ocorre mais fcilmente.Na pirlise ocorre a desvolatilizao dos componentes de menor peso molecular,diminuindo o ponto de inflamao do leo, seguida da formao de produtos de elevadopeso molecular que originam lamas, e por ltimo, carvo.

O perigo de "cracking" existe sobretudo no tubular da caldeira e da maiorimportncia evitar a qualquer sobreaquecimento do leo, devendo-se garantir que estecircule nos tubos com uma velocidade superior ao mnimo estipulado pelo construtor dosistema, e em regime de escoamento turbulento. Este problema fora a utilizao defluidos de baixa viscosidade, sobretudo a baixas temperaturas, que so as relevantes

durante o arranque do sistema de termofluido.


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Ponto de ebulio elevado (baixapresso de vapor)A variao da presso de saturao com a temperatura deve serbaixa para permitir que o leo trabalhe a temperaturas elevadas

com uma presso de vapor baixa, de modo a evitar anecessidade de pressurizao da instalao.Os leos de baixa viscosidade podem, em certos casos, ter umapresso de vapor mais elevada que os leos de mdia/ altaviscosidade, temperatura ambiente

Viscosidade CINEMTICA < 300 cSt(prximo do limite mximo da capacidade de aspirao emtermos de viscosidade para uma bomba centrfuga;Para viscosidades dinmicas superiores a 300 cSt no se usam

bombas centrfugas)


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O tanque de expanso o depsito que absorve as dilataes trmicas do

termofluido eest colocado na linha de aspirao da bomba.A 280 C o volume de fluido trmico igual a cerca de 1,2 vezes o seu volume temperatura de 15C (Uma regra de ouro indica um au mento de volume de cercade 7% por cada 100C de aumento de temperatura ).Mesmo a frio, a quantidade de leo na instalao deve ser tal que o tanque de

expanso no se encontre vazio, pelo que este deve estar equipado com umindicador de nvel.


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A produo industrial de vapor dominantemente

constituda por um sistema fechado de 4 etapas.Quando a gua vaporiza na caldeira a expanso do vaporpressuriza o sistema. O vapor sai da caldeira custa da suaprpria presso e transportado para os diferentes pontos/etapas

do processo, e as propriedades do vapor vo-se alterando.

GERAO o calor produzido na combusto aquece a gua dacaldeira

DISTRIBUIO transporte do vapor aos pontos de utilizaoTRANSFERNCIA DE CALOR o uso qualquer queseja, uma transferncia de calor. medida que transfereenergia produz-se gua condensada Reteno deCondensados.RETORNO/RECIRCULAO DE CONDENSADOS permite areutilizao parcial da energia trmica


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gua como fludo trmicoA gua a nica substncia que pode coexistir naforma de gelo, gua e vapor, em condies de pressoe temperaturas normais (~100 kPa e 0 C).

Absorve elevadas quantidades de calor, para uma dadaelevao de temperatura, mais do que qualquersubstncia orgnica comum.

Expande-se 1600 vezes, quando evapora pressoatmosfrica.

Na forma de vapor pode transportar elevas quantidadesde energia trmica.


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Objectivos do tratamento de guas para caldeiras

Preveno de incrustaes ( inibidores deincrustaes )

Preveno de corroso (inibidores de corroso)

Preveno de contaminao


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PRINCIPAIS CARACTERSTICASA CONSIDERAR NA QUALIDADE

DA GUA DE ABASTECIMENTODE CALDEIRAS

pHDurezaConcentraes elevadas de OXIGNIO, CO2

SILICATOSSlidos dissolvidosSlidos em suspensoPresena de Compostos orgnicos


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TRATAMENTO EXTERNO TRATAMENTO INTERNO


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TRATAMENTO EXTERNOPretende-se a remoo de impurezas da gua de make-up, antes daentrada para as utilidades da caldeira usando-se geralmente as seguintesOPERAES:

AMACIAMENTOEVAPORAODESAREJAMENTOUTILIZAO DE PROCESSOS DE SEPARAO POR MEMBRANAS.

TRATAMENTO INTERNOPara preveno e condicionamento de impurezas (Dureza, formaode lamas, presena de oxignio dissolvido e formao de

espuma) que resultam de reaces nas tubagens, ou dentro da caldeirapropriamente dita.O tratamento interno usado sepradamente em caldeiras de baixa pressoou, na maior parte dos casos das caldeiras de alta presso, conjugado com

o tratamento interno.


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TRATAMENTO INTERNOO tratamento interno por vezes o nico em caldeiras de baixapresso, que produzem elevadas quantidades de guacondensada

1) Esta gua condensada pode reagir com a gua de make-upcom elevada dureza, o que por acao da temperatura poddeprevenir a formao de precipitados que so causa de

incrustaes.2) O tratamento interno tem que promover o condicionamentode substncias em suspenso como sais promotores de durezaou xidos de ferro, de forma a impedir adeso desses materiais.3) Deve impedir a formao de espuma e do arraste4) Precisa eliminar o oxignio dissolvido na gua, e promoversufiente alcalinidade para evitar corroso.


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a) CALDEIRAS DE BAIXA PRESSO circuito fechado requerem pouca ou nenhuma gua de make up Operao do vapor inferior a 10-15 psi.

b) CALDEIRAS DE ALTA PRESSO

Operam com presses de vapor superiores a 10-15 psi etemperaturas de 250F.

Requerem constante fornecimento de gua de make up.


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CORROSO GALVNICA

CORROSO CAUSTICACORROSO ACDICAFRAGILIZAO PELO HIDROGNIO (Caustic embrittlement)

OXIDAO PELO OXIGNIOATAQUE POR CO2


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IND CES

1- SATURAO DE LANGLIER2 - NDICE DE ESTABILIDADE

NDICE DE

LANGLIERpHs = (9.3 + a + b) (c + d)com: a = (log( TDS ) 1) / 10

b = -13.12 * log (T) + 34.55c = log(C) 0.4

d = log(A)

LSI = pH pHsCalculador do Indice de LangelierLSI5 -- gua potencialmente incrustante

INDICE DE

ESTABILIDADESI = 2* pHs - pHSI< 6 -- gua incrustanteSI > 8 -- gua corrosiva.SI ]6-8[ gua em equilbrio.

TDS = Slidos dissilvidos totais (mg/L); T = Temperatura ( K );C = Dureza clcica (concentrao de CaCO3 mg/L);

A = Alkalinidade (expressa em concentration of CaCO3 mg/L) epH = pH da gua


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TDS - Slidos Dissolvidos Totaisporque na gua ionizam, proporcionando carga el+ectrica positivas e negativas

influenciam a condutividade da gua: mais sais>>maior transporte deelectres>>maior corroso.

TemperaturaPorque quando a temperatura aumenta, a solubilidade do Ca(OH)2, Mg(OH)2 and

CaCO3 decreases. Estas substncias formam depsitos - incrustaoes.pHO pH traduz as propores de H3O+ and OH-

Se pH > 7 h mais ies OH-;

Se o pH < 7 h mais ies H3O+;A solubilidade do xido de ferro trivalente, depende do pH: a pH baixo o xido deferro trivalente mais solvel.

BAIXOS VALORES de pH >>>>>> maior corroso

ELEVADOS pH >>>> maior possibilidade de incrustraes.

FUNDAMENTOS DO INDICE DE LANGELIER


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ESTIMATIVA DOS VALORES DESLIDOS TOTAIS DISSOLVIDOSPELACONDUTIVIDADE

Converso condutividade/TDS

425.01008.0340.0812.085.0212.042.5106.00.421.0

TDS (mg/l)Condutividade(microohm/cm)


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Minerais dissolvidos ordens de grandeza

gua do mar - 30kg/1000Lgua doce - 1 kg a 5 kg /1000L.

Para alm dos sais outras impurezas presentes nagua so mportantes quando se pensa em gerao

de vapor.


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2,068 kPa170 C

347 kPa148 C


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A produo industrial de vapor dominantemente

constituda por um sistema fechado de 4 etapas.Quando a gua vaporiza na caldeira a expanso do vaporpressuriza o sistema. O vapor sai da caldeira custa da suaprpria presso e transportado para os diferentes pontos/etapas

do processo, e as propriedades do vapor vo-se alterando.

GERAO o calor produzido na combusto aquece a gua dacaldeira

DISTRIBUIO transporte do vapor aos pontos de utilizaoTRANSFERNCIA DE CALOR o uso qualquer queseja, uma transferncia de calor. medida que transfereenergia produz-se gua condensada Reteno deCondensados.RETORNO/RECIRCULAO DE CONDENSADOS permite areutilizao parcial da energia trmica

SEPARADORES (ARMADILHAS)


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1 - MECNICOS accionados por diferencial de massas volmicas entre o vapore a gua: Uma bia (4) determina a proporo adequada lquido vapor (1). A

mistura admitida por (3) e por aco do sistema mecnico da bia (2) accionado a descarga do condensado pelo dreno (5);2 - TERMOSTTICOS accionados por diferenciais de presso/temperatura.3 - TERMODINMICOS accionados por diferenas de presso volume.

SEPARADORES (ARMADILHAS)DE CONDENSADOS


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PURGA DE CALDEIRAS = BLOW-DOWN

A purga de caldeiras um passo importante do tratamento deguas de caldeiras e tem como objectivo reduzir as impurezas dagua que utilizada na caldeira, quando existe recirculao.

Excessode purga >>> desperdcio de energia;Deficitde purgas >>> promove incrustaes.

No existem regras fixas, mas as taxas variam entre 1% e 25%da gua de abastecimento da caldeira.


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RECUPERAO DE CALOR DA PURGA DE CALDEIRA

FLASH STEAM - excesso de vaporRECUPERAO do calor de excessos de distribuio do vapore da energiaremanescente dos condensados, para efeitos de aquecimento da gua de make-up.


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Neste sistema s a componente de vapor do blowdown utilizada para pr-aquecimento a gua de reposio da caldeira; o condensado descartado,

eventualmente depois de refrigerado com gua fria para poder cumprir oslimites de temperatura de descarga



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O flash steam and hot blowdown condensate so utilizados para pr-aquecera gua de make-up, pelo uso de um trocador de calor; necessitando que haja

coincidncia entre a entrada da gua de make-up e a descarga da caldeira.


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Neste caso adicionado um depsito de gua fria que recirculando no trocador de calortorna desnecessrio o sincronismo entre o blowdown e o make-up.


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Estimating SavingsA poupana de energia resultante da recuperao de calor de descargas (purgas) de caldeira

depende da capacidade da caldeira (kg de vapor por hora), presso, mtodo e frequncia dasdescargas e do custo do combustvel.Descargas contnuas so via de regra 5 10% de capacidade.The blowdown BTU value varies with boiler steam pressure; the higher the boiler pressure thehigher amount of higher value flash steam.Assume 25% flashes to steam and remainder is hot condensate for boilers under 300 psi.

The General Formulas:Average Boiler Capacity in pounds per hour of steam x 5% = Blowdown volume(Blowdown volume x 25% x 1,200 BTUs per Pound) + (Blowdown volume x 75% x 140 BTUs perPound) = Total BTUs por hora no blowdown{[Total BTUs por hora no blowdown] x 90% Efficiency / (1,000,000 BTUs x Boiler Efficiency) } =

Millions of BTUs per Hour RecoveredMMBTUs x $ per MCF = Hourly Savings

EXAMPLE: 50,000 lbs per hour boiler at 200 psi steam with continuous blowdown50,000 lbs per hour x 5% = 2,500 lbs per hour blowdown

(2,500 x 25% x 1,200 BTUs) + (2,500 x 75% x 140 BTUs) = 1,012,500 BTUs per hour in Blowdown(1,012,500 x 90% Efficiency) / (1,000,000 x 85%) = 1.07 MMBTUs per hour1.07 x $7.00 per MCF = $7.50 per hour = $180 per day = $5,400 per month

NOTE: In some applications the amount of flash steam produced by the blowdown recovery canexceed the amount of steam needed by the deaerator. This can lead to excessive steam ventingfrom the deaerator and reduce the overall saving potential of the recovery system.

1 BTU ~ 1 054 1 060 J (joules) ~ 2.931 10-4 kWh


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Estimating SavingsA poupana de energia resultante da recuperao de calor de descargas (purgas) de caldeira

depende da capacidade da caldeira (kg de vapor por hora), presso, mtodo e frequncia dasdescargas e do custo do combustvel.Descargas contnuas so via de regra 5 10% de capacidade.The blowdown BTU value varies with boiler steam pressure; the higher the boiler pressure thehigher amount of higher value flash steam.Assume 25% flashes to steam and remainder is hot condensate for boilers under 300 psi.

The General Formulas:Average Boiler Capacity in pounds per hour of steam x 5% = Blowdown volume(Blowdown volume x 25% x 1,200 BTUs per Pound) + (Blowdown volume x 75% x 140 BTUs perPound) = Total BTUs por hora no blowdown{[Total BTUs por hora no blowdown] x 90% Efficiency / (1,000,000 BTUs x Boiler Efficiency) } =

Millions of BTUs per Hour RecoveredMMBTUs x $ per MCF = Hourly Savings

EXAMPLE: 50,000 lbs per hour boiler at 200 psi steam with continuous blowdown50,000 lbs per hour x 5% = 2,500 lbs per hour blowdown

(2,500 x 25% x 1,200 BTUs) + (2,500 x 75% x 140 BTUs) = 1,012,500 BTUs per hour in Blowdown(1,012,500 x 90% Efficiency) / (1,000,000 x 85%) = 1.07 MMBTUs per hour1.07 x $7.00 per MCF = $7.50 per hour = $180 per day = $5,400 per month

NOTE: In some applications the amount of flash steam produced by the blowdown recovery canexceed the amount of steam needed by the deaerator. This can lead to excessive steam ventingfrom the deaerator and reduce the overall saving potential of the recovery system.

1 BTU ~ 1 054 1 060 J (joules) ~ 2.931 10-4 kWh


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NOTA

Como se ver muitas aplicaes do vaporrecuperado no flash, pelas purgas de caldeira,excedem a quantidade de vapor necessria aosistema desajerador/desgaseificador.

Se isto acontecer haver excesso de vapor quedeve ser libertado, ao nvel do

desajerador/desgasificador, reduzindo apoupana de energia.


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Boiler turndown is a ratio of capacity (massa de vaporproduzida na unidade de tempo) at full fire to its lowest

firing point before shut-down.

Old boilers may have only two firing positions, low and

high.

If a 1 million BTU boiler can fire as low as 100,000

BTUs, then it has a 10:1 turndown ratio.


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Tipes de materiais utilizados na Troca Inica

Tipos de sistemasde troca inica: trocadores catinicos (Ca++ e Mh++. )e trocadoresaninicos (CO3 e SO4).

Os Zeolitos so caties de troca compostos de sdio, alumnio e slica; mas h tambmmateriais orgnicos ou resinosos.

Os materiias aninicos so usualmente orgnicos, e h materiais de base fraca queremovem cidos fortes por um processo mais parecido com adsoro do que de trocainica mas retm slica e dixido de carbono e os de base forte . Estes trocadoresaninicos so geralmente operados numa base fraca ou com carbonatos.

.

Os permutadores de troca aninica com base em solues bsicas reduzem a apresena de slica e de dixido de carbono.


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Boiler turndown is a ratio of capacity (massa de vaporproduzida na unidade de tempo) at full fire to its lowest

firing point before shut-down.

Old boilers may have only two firing positions, low and

high.

If a 1 million BTU boiler can fire as low as 100,000

BTUs, then it has a 10:1 turndown ratio.


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CALDEIRAInputde energiado combustvel

(100%)

Perdas porconvecoRadiao (4%)

Perdas da emissoe gases na chamin(18%)

Perdas no blowdown=descargas/purgas da caldeira (~3%)

Output de energia

Eficincia trmica daCaldeira 75 a 77%


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Cerca de 5% da alimentao (combustvel) de uma caldeira pode serpoupado pela instalao de um economizador

Green House GasPotential Relative

EffectSourceEmission


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Potentialcarcinogens,

Global Warming

Compounds in fuel orcombustion air containing

halogens (Chlorine, fluorine,bromine and iodine)

Halogenated andChlorinated

Compounds

Unknown andPotentialCarcinogens

Impurities in fuelTrace Elements

Smog,Respiratory

Hazard

Unburned carbon from fuel,including ash and dirt

Particulates (Dust,Soot, Fumes)

Localized FogHydrogen in fuel mixing withoxygen in the combustionprocess

H2O (Water Vapor)

21Global WarmingNatural Gas LeaksCH4 (Methane)

SmogLeakage and evaporation ofliquid fuels

VOCs (VolatileOrganicCompounds)

310Global WarmingBy-product of somecombustion processes

N2O (NitrousOxide)

Acid RainBy-product of mostcombustion processesNOx (NitrousOxide)

Smog, Acid RainCombustion of sulphur in fuel(Sulphur is NOT a componentof natural gas)

SO2 (SulphurDioxide)

SmogIncomplete combustion ofcarbon in fuel

CO (CarbonMonoxide)

1Global WarmingComplete combustion of

carbon in fuel

CO2 (Carbon

dioxide)

to CO2


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Desgasificador/DesarejadorRemove gases no condensveis da gua dealimentao.

Promove-se o aquecimento da gua de makeup(reconstituio/reposio)Minimiza-se a solubilidade de gases no

condensaveis (ex. Oxignio, CO2, H3, etc.).Pr aquece-se a gua que ir ser utilizada(injectada) na caldeira.

Os desarejadores so instalados a cota elevada para criaremcarga favorvel ao funcionamento das bombas de gua queabastecem a caldeira, contornando a possibilidade de

ocorrerem eventuais condies de cavitao.


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LIMITAES A gua deve estar livre de impurezas que possamEntupir os aspersores ou colmatar os tabuleiros.


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TROCA INICA


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TROCA INICA

TROCA INICA


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TROCA INICA

DESMINERALIZAO


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DESMINERALIZAO

CONDIES DE OPERAO DE UMA


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CALDEIRASe a gua de alimentao for dura (sais de clcio e magnsio)e no for devidamente tratada quimicamente, promoveincrustraes, prejudica a transferncia de calor e a eficincia dacaldeira, torna importante aumento de requncia de trabalhos delimpeza e de manuteno preventiva.

Se a gua contem gases dissolvidos, particularmente

oxignio, surge a corrosonas paredes da caldeira e na tubagem. Se o pH da gua for baixo a soluo cida ataca as superfciesmetlicas. Se o pH for demasidamente elevadoprove osugimento de espuma.

Fragilizao por hidrognio(caustic embrittlement ou causticcracking) resulta da excessiva concentrao de hidrxido desdio especial cuidado deve ser tido com as estremidades das

tubagens.


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TRATAMENTO DE GUA DEABASTECIMENTO DE CALDEIRAS

>> REMOO

Sais minerais (promovemincrustaes)Gases (corroso)

Materiais particulados (abraso)


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Sais minerais que promovem incrustaes:

FERROCLCIO

MAGNSIOSLICA


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Quando se utilizam economizadores de energiadeve utilizar-se um desajerador.

A corroso por oxignio (picadas) a maiorcausa de falhas do economizador.

O economizador deve ser protegido por umsupressor de oxignio sulfito de sdioadicionado a 3-10 ppm na gua de alimentao,associando a uso de soda caustica at termos a

gua de alimentao com pH (8,0 9,0)

Abaixo de 900 psi (~62 atmosferas) no perigoso o uso de excesso sulfito de sdio (at200 ppm)

1psi = 6894,8 Pa

SQ S S O G


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ESQUEMA DE UM SISTEMA DE TRATAMENTO DE GUA

ABASTECIMENTO DE CALDEIRAS


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Tratamento externo

TRATAMENTO EFECTUADO NOSISTEMA DE ABASTECIMENTODE GUA

Clarificao (remove slidos, verylarge boiler systems)Filtrao (remove slidos)Amaciamento e Desmineralizao(removes sais minerais)DealkalizationDesajerao and Heating (removesoxygen and other corrosive gases)

Tratamento Interno

Adio de correctivos qumicos(controlo de pH, Remoo de

Oxignio, outros)Purga (remove slidos acumuladospor recirculao de gua emebulio)

WATER CHEMICALS


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OXYGEN SCAVENGERSSulfites - typically for boilers up to 800 psi; sulfites react with oxygen to formsulfates that are removed from the boiler via blowdown. There are two formsof sulfite: Catalyzed - uses a catalyst to improve reaction time; Non-catalyzed- slower reaction time and must be used in hot water

Hydrazine - typically for boilers over 800 psi. At pressure higher than 800psi, sulfite begins to break down into acidic gases of sulfur. Sulfite also creates

additional Total Dissolved Solids (TDS) which is a problem for high pressureapplications.

Hydrazine removes O2 without producing acidic gases or TDS, but isconsidered a possible carcinogen.

HYDROXIDESSodium Hydroxide - NaOH or Caustic Soda, or Soda Ash - used tomaintain boiler water pH in the 10.0 - 11.5 range.Hydroxide increase boiler alkalinity to prevent acidic corrosion. If heavy scale is present, caustic soda can accumulate to cause Caustic Attack.Calcium-Hydroxide - reacts with calcium and magnesium bicarbonates toform sludge that is removed via blowdown.

Phosphates


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PhosphatesPhosphate treatment causes calcium and magnesium to precipitate intosludge where it can be removed via blowdown.

Filming AminesFilming amines function by forming a protective barrier against both oxygenand carbon dioxide attack. These amines form films directly with thecondensate line metal and develop a barrier to prevent contact of thecorrosive condensate with the return piping. By design, film formers havebeen developed to function best at a pH of 5.5-7.5.In addition, these amines are highly surface-active and will slough looselyadherent iron oxide and other corrosion products back to receiving points orto the boiler. Care must be exercised with the feed of filming amines.

Combination Amines.Over the past several years, combinations of filming and neutralizing amineshave been shown to be extremely effective, particularly in complex systems.While the combination amine is still functionally a filmer, the neutralizingamine portions provide for reduction in fouling potential and more uniformcoverage of the filmer.Filming amines and combination amines are generally fed to steam headers.Dosages are based on steam production.


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POLMEROSPolymers are long, complex molecules that attach to impurities and preventthem from sticking to boiler metal to form scale. This creates TDS that areremoved via blowdown.

QUELANTESChelants can prevent scale from forming and over time, remove existing scale.Chelants in contact with 02 is corrosive.It must therefore be used in an 02- free environment.

Neutralizing AminesNeutralizing amines hydrolyze in water to generate the necessary hydroxideions required for neutralization of the carbon dioxide.The normal approach to treating systems with these amines is to feed sufficientquantity to neutralize the carbon dioxide and then provide small additionalamounts to buffer the pH to 8.5 or 9.0.

At this pH, continued preservation of the magnetite film (boiler metal) is alsoachieved.It is also implied that corrosion will not exist at a pH>8.0-8.5.


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For example: consider a 500 hp boiler with a gas input of 20 million BTUs perHour.

20,000,000 BTUs x 5% = 1,000,000 BTUs (100% Load Factor)1,000,000 BTUs / (1,200 BTUs per Gallon of 200F water) = 833 Gallons per Hour(1,000,000 BTUs / 80% efficiency) = ~1.2 MCF x $7.00 per MCF Natural Gas =

$8.40 per Hour ValueSavings is reduced by 50% for a 50% Load Factor, etc.

If there is a need for that much hot water, the savings potential of $8.40 perhour would be multiplied by the number of boiler run hours, or the number of

hours that the hot water can be used. In each application, be sure to considerthe boiler Load Factor, the efficiency that the hot water is otherwise producedat, the cost of natural gas, and the installation cost of the equipment.If the economizer would be used to heat boiler make-up water, it is necessaryto determine the volume and temperature at the inlet of the economizer. The

lower the amount of condensate return, the higher the volume of make-upwater and the higher savings potential.An economizer that recovers 5% of boiler input should easily have a 2 yearpayback in a year-round application.


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1 psi = 6.894757 kPa ~ 6 895 Pa


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FORNECIMENTO DE AR


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Um dos cuidados necessrios aofuncionamento de uma caldeira, para evitarmosproblemas srios de combusto estabelecer osuprimento de ar adequado.

1. AR DE COMBUSTO = (n de HP*) x (8 CFM/HP) =nHPx0.2265 m3/HP.

2. AR DE VENTILAO = (n de HP*) x 2 CFM/

3. VOLUME TOTAL DE AR REQUERIDO =(n de HP*) x 10 CFM/HP

*HP refere-se to the total de potncia de caldeiras instaladas.

ALERNATIVA 4 a 6 square inches/HP (0,00064516 m2/ HP)

Ex. 75 Horsepower Boiler X 5 Square Inches1 HP= 735.4988 watts


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Boiler water carry-over is the contamination of the steam with boiler-water solids.Bubbles or froth actually build up on the surface of the boiler water and pass outwith the steam. This is called foaming and it is caused by high concentration ofany solids in the boiler water. It is generally believed, however, that specific

substances such as alkalis, oils, fats, greases, certain types of organic matterand suspended solids are particularly conducive to foaming. In theory suspendedsolids collect in the surface film surrounding a steam bubble and make it tougher.The steam bubble therefore resists breaking and builds up foam. It is believedthat the finer the suspended particles the greater their collection in the bubble.


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Priming is the carryover of varying amounts of droplets of water in thesteam (foam and mist), which lowers the energy efficiency of the steam andleads to the deposit of salt crystals on the super heaters and in the turbines.Priming may be caused by improper construction of boiler, excessive ratings,

or sudden fluctuations in steam demand. Priming is sometimes aggravatedby impurities in the boiler-water.Some mechanical entertainment of minute drops of boiler water in the steamalways occurs. When this boiler water carryover is excessive, steam-carriedsolids produce turbine blade deposits. The accumulations have a

composition similar to that of the dissolved solids in the boiler water. Primingis common cause of high levels of boiler water carryover. These conditionsoften lead to super heater tube failures as well. Priming is related to theviscosity of the water and its tendency to foam. These properties aregoverned by alkalinity, the presence of certain organic substances and by

total salinity or TDS. The degree of priming also depends on the design ofthe boiler and its steaming rate.


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gua de Reposio (Makeup) gua bruta, gua macia ou guadesmineralizada

A presso do vapor de uma caldeira varia entre (0,5 -100 bar) e determina a energia gerada e a capacidade


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100 bar) e determina a energia gerada e a capacidade,e tambm a qualidade da gua de abastecimento.

A regra geral que quanto maior for a presso

necessria ao vapor de gua que se quer produzir, maisrigorosa a qualidade da gua.

Os principais 4 problemas que surgem

numa caldeira so: Incrustrao/Scaling Corroso/Corrosion Formao de espuma e Escorva/Foaming andPriming(gotculas de gua no caudal de vapor) Arraste de minerais volteis/Carryover

Parmetros da gua de


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abastecimento (feed water)pHDurezaGases Dissolvidos (Oxignio e Anidrido

de Carbono)Silicatos

Slidos em suspensoConcentrao de substncias organicas


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What is an External Treatment?


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Treatment of water that are done outside of the boiler is called pre-boiler or externaltreatment. The main physical methods for improving quality of water for boilerinclude flocculation, clarification, deaeration, oil removal, colour removal,suspended solids removal and blow down. When preparing water for boilersoperated at less than 150 psi, all necessary chemical treatments can be

accomplished in a clarifier, but as pressure increases; the quality of feed watermust improve. The purpose of external treatment is to reduce suspended solids,demineralize the feed water and remove silica. This purpose can be achieved byCoagulation with chemicalsDemineralization/ Reverse osmosis/ Electrodialysis (cold lime, soda process,

hotlime-soda process, mixed bed exchange)Silica removal (coagulation with chemical, Demineralization, Reverse Osmosis,Electrodialysis)


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1. Dissolved Gases :the two gases which cause corrosion are oxygen and carbon dioxide. The carbondioxide does so simply by dissolving in the water and forming a weak carbonic acidwhich attacks the metal in feed systems, boiler or condensate system. Oxygen ispresent in all waters, so that red iron oxide forms on a mild steel surface immersed

in water. This rusting or, as we call it, corrosion triunes until the metal is corrodedaway. If the amount of oxygen in the water is restricted, the oxide film does not formso readily; but instead, the surface of the steel tarnishes. This tarnish is usually thedevelopment of a thin film of iron oxide on the metal surface which is not so fullyoxidized as the red iron oxide, and is more dense, thus tending to resist further

corrosive attack. In water of increasing alkalinity, the oxide film becomes morestable and gives more protection to the steel, but until a definite alkalinity is reached,it still tends to break down in selective areas, where pits will develop.


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Calcium and magnesium salts :There are two forms of hardness; temporary and permanent.

Temporary hardness is due bicarbonates of calcium and magnesium which breakdown to carbonates when the water is boiled. In the boiler the following chemicalreaction takes place : Calcium Bicarbonate + heat. Calcium Carbonate+carbondioxide+water. Calcium and magnesium bicarbonate are soluble in water but thecarbonates are insoluble and therefore precipitate as a fine white powder. This

precipitate will bake unto the heating surface of a boiler and form a scale.Permanent hardness is due to calcium and magnesium sulphates, chlorides andnitrates, and these salts cannot be removed by boiling. However, under boilerconditions (resulting in successive concentrations of these hardness salts) thesolubility of these salts is soon exceeded and they deposit on the hottest part of

the heating surface. The salts of magnesium that form permanent hardnesssometimes tend to cause corrosion instead of hard scale formation, e.g.magnesium chloride in an untreated boiler hydrolyses to form corrosivehydrochloric acid.

What is an External Treatment?


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Treatment of water that are done outside of the boiler is called pre-boiler or externaltreatment. The main physical methods for improving quality of water for boilerinclude flocculation, clarification, deaeration, oil removal, colour removal,suspended solids removal and blow down. When preparing water for boilersoperated at less than 150 psi, all necessary chemical treatments can be

accomplished in a clarifier, but as pressure increases; the quality of feed watermust improve. The purpose of external treatment is to reduce suspended solids,demineralize the feed water and remove silica. This purpose can be achieved byCoagulation with chemicalsDemineralization/ Reverse osmosis/ Electrodialysis (cold lime, soda process,

hotlime-soda process, mixed bed exchange)Silica removal (coagulation with chemical, Demineralization, Reverse Osmosis,Electrodialysis)


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What is an Internal Treatment?There are number of treatments that are made within the boiler to minimize theadverse effects of small concentration of components that remain in the feed waterafter the external treatment. In spite of various external treatments, it is not possible

to attain an absolute perfect quality of boiler feed water. Chemical treatment orinternal treatment of water inside the boiler is essential to take care of variousimpurities entering into the boiler such as hardness, dissolved solids, oxygen, andsilica.

In many cases, external treatment of water supply is not necessary specifically in lowor moderate pressure boilers or where large amount of condensed streams are usedor when raw water available is of very good quality.


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Silica :Silica forms scale in a similar way to the permanent hardness salts. When the scale

formed is a mixture of silica, calcium and magnesium salts, it is very hard andtherefore presents a difficult problem at inspection time.4. The suspended and dissolved solids :The suspended and dissolved solids cause foaming by becoming absorbed unto thewalls of individual bubbles so that small bubbles, instead of coalescing to form large

ones and bursting early, repel one another and build up a large volume of smallbubbles. If these bubbles burst near the steam outlet, the spray is taken over with thesteam. If the bubbles do not burst high in the steam space, the foam can be drawnover with the steam.


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ARRASTE, ESPUMA E PRIMING

Fontehttp://www.arvanitakis.com/en/bHP/priming,_foaming_and_carry_over.htm

ARRASTE


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Descreve genericamente a sadade gua da caldeiraconjuntamente com o vaporfoaming, priming ormechanical inefficiencies.

Resulta da presena de

impurezas que aumentam atenso superficial o que inibe aseparao do vapor de gua dagua, o que causa ESPUMA

(foaminga).Precisa-se de controlar eMINIMIZAR a concentrao dosslidos solveis totais (TDS).

FOAMING


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BOLHA NORMAL BOLHA COM ARRASTE

Na produo de vapor h formao contnua de bolhas que rebentam na interfacelquido-vapor.Se a velocidade (TAXA) de chegada interface, das bolhas que se formam no interiordo intlquido for maior do que a remoo do vapor, as bolhas acumulam-se comoespuma.

Steam released from the bursting bubbles move towards the steam outlet carrying withit smaller water droplets and taking with it any foam.The steam also drags the surface of the boiler water towards the steam outlet so thatthe water level at that point can be higher than elsewhere, depending on the positionsof the level controls this may cause the feed pumps to deliver water and thus raising

the water level further.

Priming (escorva)


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Nvel de gua sobe >>>Espao para o vapor desce >>>A velocidade de sada do vapor

da interface sobe>>>As bolhas arrastam gotas degua para fora juntamente com

o vapor.

Causas:-aumento sbito da demanada devapor-Operao da caldeira a abaixo da

presso recomendada.

During the conditioning process, which is an essential complement to the watertreatment program, specific doses of conditioning products are added to the water.The commonly used products include:


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Phosphates-dispersants, polyphosphates-dispersants (softening chemicals):reacting with the alkalinity of boiler water, these products neutralize the hardnessof water by forming tricalcium phosphate, and insoluble compound that can bedisposed and blow down on a continuous basis or periodically through the bottomof the boiler.

Natural and synthetic dispersants (Anti-scaling agents): increase thedispersive properties of the conditioning products. They can be:Natural polymers: lignosulphonates, tanninsSynthetic polymers: polyacrilates, maleic acrylate copolymer, maleic styrenecopolymer, polystyrene sulphonates etc.

Sequestering agents: such as inorganic phosphates, which act as inhibitors andimplement a threshold effect.Oxygen scavengers: sodium sulphite, tannis, hydrazine, hydroquinone/progallol-based derivatives, hydroxylamine derivatives, hydroxylamine derivatives, ascorbicacid derivatives, etc. These scavengers, catalyzed or not, reduce the oxides and

dissolved oxygen. Most also passivate metal surfaces. The choice of product andthe dose required will depend on whether a deaerating heater is used.Anti-foaming or anti-priming agents: mixture of surface-active agents thatmodify the surface tension of a liquid, remove foam and prevent the carry over offine water particles in the steam.

C i1 Di l d

EFFECT ON A BOILERIMPURITY


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Contribute to, or cause,carryover (*)

4. Suspended solidsand dissolved solids

Can form a very hardscale.

3. Silica

These salts are the'hardness in the boiler.

Some salts can also causecorrosion

2. Calcium salts and

magnesium salts

Corrosion1. Dissolved gases

Calcium and magnesium salts :There are two forms of hardness; temporary and permanent.


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Temporary hardnessis due bicarbonates of calcium and magnesium which break down to carbonateswhen the water is boiled. In the boiler the following chemical reaction takes place :Calcium Bicarbonate + heat. Calcium Carbonate+carbon dioxide+water. Calcium

and magnesium bicarbonate are soluble in water but the carbonates are insolubleand therefore precipitate as a fine white powder. This precipitate will bake unto theheating surface of a boiler and form a scale.Permanent hardness is due to calcium and magnesium sulphates, chlorides andnitrates, and these salts cannot be removed by boiling. However, under boiler

conditions (resulting in successive concentrations of these hardness salts) thesolubility of these salts is soon exceeded and they deposit on the hottest part of theheating surface. The salts of magnesium that form permanent hardness sometimestend to cause corrosion instead of hard scale formation, e.g. magnesium chloride inan untreated boiler hydrolyses to form corrosive hydrochloric acid.


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http://hamadaboiler.com/en/water.html#15

Em Suspenso

(ppm)ALKALINIDADE

(ppm)Slidos totais

(ppm)PRESSO

MANOMTRICA NACALDEIRA (kPa)


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0.55100500over 13780

1.5105075010335-137802.5202010006890-10335

8402512506200-6890

20603001505170-6200

3510040020004135-51705015050025003100-4135

9025060030002070-3100

12530070035000-2070

silica*solids(ppm)(ppm)(kPa)

(*) Silica limits based on limiting silica in steam to 0.02-0.03 ppm.


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What is Caustic Cracking? = caustic embrittlementFissuras microscpicas no metal sob elevada tenso..

causada pela presena de slica e elevadas concentraes de sais.

X500

What is Boiler Water Carryover?Boiler water carry-over is the contamination of the steam with boiler-water solids. Thereare four common types of boiler-water carry-over.In one bubbles or froth actually build up on the surface of the boiler-water and pass out

with the steam This is called foaming and can be compared to the stable foam found on


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with the steam. This is called foaming and can be compared to the stable foam found onbeer.In the second type small droplets of water in the form of spray or mist are thrown up intothe steam space by the bursting of the rising steam bubbles at the steam releasesurface. This is sometimes called aquaglobejection Eand is like ginger ale or

champagne where no stable foam is formed but droplets of liquid are ejected from theliquid surface.The third condition of carry-over, called priming, is a sudden surge of boiler-water thatcarries over with the steam, similar to the effects produced in uncapping a bottle ofcharged water. stem contamination may also occur from leakage of water throughimproperly designed or installed steam separating equipment in a boiler drum.

What Causes Foaming?Very high concentrations of any solids in boiler-water cause foaming. It is generallybelieved, however, that specific substances such as alkalis, oils, fats, greases, certaintypes of organic matter and suspended solids are particularly conducive to foaming.

What Causes Priming?Priming may be caused by improper construction of boiler, excessive ratings, or suddenfluctuations in steam demand. priming is sometimes aggravated by impurities in theboiler-water

Amaciamento de gua com carbonato

de Sdio (barrilha)


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de Sdio (barrilha)Uso de barrilha (carbonato de sdio) para amaciar gu com DUREZAPERMANENTE proveniente sulfato ou de cloreto de clcio

Sulfatode Sodio

Carbonato declcio

======>Sulfato declcio

Carbonato desdio

Na2SO4+CaCO3======>CaSO4+Na2CO3

Cloreto deSodium

Carbonato declcio

======>Cloreto declcio

Carbonatode sdio

2NaCl+CaCO3======>CaCl2+Na2CO3

Forma uma lamaseparvel da guapor filtrao

O carbonatode sdio irritante

Following is a list of some of the hazards that can occur in a boiler room:

Safety or safety relief valves that do not operate properly can cause a buildupf b il


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Safety or safety relief valves that do not operate properly can cause a buildupof boiler pressure.Becoming asphyxiated or injured while cleaning boilers because properprocedures were not followed.Slippery floors due to inadequate clean-up of oil and grease spills.

Improper storage of boiler chemicals.Working platforms and ladders not provided or in poor repair.Energy controlling devices such as switches, valves, etc. not being properlylocked and/or tagged out before working on equipment controlled by them.Leakage at gas and fuel supply lines.

Flame failure, fuel cut-off, and other controls not working properly.Insufficient areas of clearance around boilers.Improper welding operations and repairs.Improperly placed exits that prevent egress of workers in the event of asteam leak or explosion.

Unguarded pump shafts and unguarded nip points


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De acordo com a lei portuguesa obrigatria a contratao de

fogueiros para a operao de caldeiras de vapor, o que noacontece com as caldeiras de termofluido.

Naturalmente que da advm outra das grandes vantagens dos

sistemas de termofluido atravs da reduo dos custosde mo de obra, principalmente se se estiver a trabalhar porturnos.

tratamento de Água e problemas ocasionados

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