570 likes | 1.3k Views
BOILER WATER TREATMENT THE POLYAMINE SOLUTION. Water cycle in the boiler house. RAW WATER. SOFTENER. Superheater. uses. Water meter. Deaerator. FFEED TANK. condenser. BOILER. BLOWDOWN. Dosing tank. CONDENSATE RETURN. MAIN PROBLEMS. Scaling Corrosion Carry over.
E N D
Water cycle in the boiler house RAW WATER SOFTENER Superheater uses Water meter Deaerator FFEED TANK condenser BOILER BLOWDOWN Dosing tank CONDENSATE RETURN
MAIN PROBLEMS • Scaling • Corrosion • Carry over
Raw water composition Including Sand, mud, colloidal organic material, and so on, Suspended solids Organic material in solution Organic acid, vegetation rejection,… Cations : Anions : Dissolved salts Calcium Ca2+ Magnesium Mg2+ Sodium Na+ Potassium K+ etc... Bicarbonates HCO3- Chlorides Cl- Sulfates SO42- Nitrates NO3- etc... Dissolved gas Oxygen, carbonic gas, nitrogen Micro-organisms Algae, bacteria, fungi
Scale-forming salts mg/L CaSO ,2H O 4 2 2200 (gypsum) CaSO 4 (anhydrite ) CaSO ,1/2H O 4 2 (semi-hydrate) 300 CaCO 3 100 40 60 180 °C
SILICA SiO2 in steam in ppm SiO2 in boiler (mg/L) Pressure in bar
Basic corrosion process Anodic reaction H O 2 Fe - 2+ OH Fe + 2 - OH - - + 2 e OH Fe(OH) 2 + + H + Cathodic reaction 2H H - + 2 e 2 2 e With dissolved oxygen : - - ® 4 e + O + 2 H O 4 OH 2 2
Local oxygen corrosion Oxygen cannot reach the metal under the deposit, which creates an anodic area. O 2 O 2 O 2 - OH ++ Fe - OH - e - e - e The cathodic reaction is taking place where oxygen can reach the metal. Metal : Iron
High temperature corrosion 3 Fe + 4 H2O Fe3O4 + 4 H2 Shikorr reaction : This reaction is catalysed by dissolved oxygen.
CO2 production by softened water • BICARBONATES ARE DECOMPOSED IN CARBONATES BY HEAT WITH PRODUCTION OF CO2 • CARBONATES ARE HYDROLYSED INTO CAUSTIC SODA WITH PRODUCTION OF CO2 THE REACTIONS : • 2NaHCO3 Na2CO3 + CO2 + H2O • Na2CO3 + H2O 2 NaOH + CO2
Bicarbonate decomposition % decomposition 100 100 °C 90 °C 50 30 60 90 120 time mn REACTION 1 :2NaHCO3Na2CO3 + CO2 + H2O
Carbonate decomposition % Hydrolysis 100 50 10 20 30 40 50 P in bars REACTION 2 :Na2CO3 + H2O2 NaOH + CO2
pH control of feedwater and boiler water Avoid precipitation of scaling salts: calcium carbonate, silica, iron, copper Internal protection of boiler tubes and drums Protection of condensate return lines PURPOSE OF BOILER WATER TREATMENT
Phosphates Oxygen scavengers Dispersants, anti-scaling agents Neutralizing amines TRADITIONAL TREATMENT
Oxygen scavengers MAIN OXYGEN SCAVENGERS • sulfites : • Na2SO3 + ½ O2 Na2SO4 • hydrazine : • N2H4 + O2 N2+H2O • tanins
Toxicity: hydrazine, morpholine Corrosion of copper and copper alloys Extra salinity added: phosphates, sulfites Problems due to feedwater injection in steam MAIN DISADVANTAGES
A combination of 2 main actions pH control Filming protection POLYAMINE ALTERNATIVE
R-NH- CH2 3-n-NH2 n = 0 to 7 example : octadecylamine n = 0 R = straight carbon chain with C12 minimum and C18 predominant FILMING POLYAMINES
VARIOUS ACTIONS • ANTI-SCALING EFFECT • ADSORPTION : FILMING EFFECT • PSEUDO-COMPLEX FORMATION WITH METALS • DROP CONDENSATION
ADSORPTION 3 3 1. Adsorption 2 2 2. Ion - ion 1 1 1 3. Hydrophobic bond
PSEUDO-COMPLEXFORMATION CH3 CH3 CH2 CH2 CH2 CH2 H H N N O O H H Fe Fe H H O O O O H H Fe Fe
THE POLYAMINE FILM Polyamines form a protective film on the metal surface. This film has been evidenced by means of electrochemical measurements of corrosion and particulary by electrochemical impedance diagrams.
INVESTIGATION OF THE FILM EXPERIMENTAL PROCEDURE Potentiostat I mA E mV Auxiliary electrode (Pt) Reference electrode Rotating disc electrode (steel)
IMPEDANCE DIAGRAM - jG (.cm2) HF loop : film evidence R (.cm2) Re Rp Cd CHF Cd Re Re RHF Rp Rp
Protection of boilertubes • Polyamines stabilize the magnetite layer formation on the tubes of steam generators. • The study of the effect of POLYAMINE products on the Shikorr reaction (magnetite production) proves the efficiency of polyamines against corrosion.
Magnetite production : experimental procedure Emulsion water/steam 24 % Incondensable gases H2 Expansion condensation cooling Boiler tube : = 23 w/cm2 P = 100 bars T°C = 315 °C Make - up : demineralized water 3 Fe + 4 H2O Fe3O4 + H2 Shikorr reaction
Stability of the magnetite layer H2 as vpm (volume per million) Magnetite production POLYAMINE injection 10 2 vpm during 72 hours 2 time
HEAT EXCHANGE • The polyamine film formed on metal surfaces does not affect the thermal exchange. • Presence of polyamines increases the yield of condensers.
THERMAL EXCHANGE in w/cm.°C
DROP CONDENSATION Dh (%) 5 4 3 2 1 Film condensation ppm ODA Drop condensation 0 1 2 3
Toxicity of hydrazine: LD 50 = 60 mg / kg of weight Carcinogenic Inocuity of the polyamine: LD 50 > 2000 mg / kg Non carcinogenic Toxicity vs inocuity
Efficiency Simplicity Hydrazine free Non toxic Reduction of blowdown Improvement of condenser yield Cost-effective CONCLUSIONS