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Carbohydrazide vs Hydrazine: A Comparative Study
INTRODUCTION
The Saline Water Conversion Corporation (SWCC) pro-
duces power and drinking water through its dual-purpose
plants. At Al-Jubail, there are three powerhouses, namely,
Phase-I, Phase-II A and Phase-II B. Phase-I consist of
6 boilers and 6 turbines, each producing 60 MW, and
Phase-II A and B each have 6 boilers and 5 turbines, each
producing 130 MW. Each powerhouse of Phase-II has a
spare boiler. The total power production at Al-Jubail
Power Plant is 1 660 MW. The steam from each boiler in
Phase-II is sent to 4 desalination plants for heating sea -
water.
The core of the powerhouse is the boiler, which produces
high-pressure (HP) steam that drives the turbines for
generating electricity. Boiler feedwater is the returned
condensate coming from the turbines through brine
heaters and turbine condensers, and make-up water
produced from a demineralization plant is added to
replace evaporation and blowdown losses.
Due to the mixed-metallurgy feedwater system with
copper-based alloys in the high-pressure heater, the brine
heater and the dump condenser (Table 1), the feedwater
chemistry must be an all-volatile treatment under reducing
conditions (AVT(R)) with the addition of a solid alkalizing
agent (phosphate) to the boiler drum [1,2]. This treatment
involves the addition of an amine (morpholine) and a
reducing agent (usually hydrazine or one of the acceptable
substitutes) to the condensate or feedwater of the plant.
Among the many oxygen scavengers available in the
market are hydrazine, carbohydrazide, n-diethyl hydroxyl -
amine (DEHA), hydroxyquinone and erythorbic acid [3–7].
Hydrazine has been extensively used as an effective
oxygen scavenger [6] and was utilized in many of the high-
pressure boilers of the SWCC. But the reaction kinetics
has shown that at low temperatures the scavenging effect
of hydrazine is quite slow [8,9]. Studies have indicated
some difficulties both of a technological nature and those
connected with its toxicity. The SWCC operation and
maintenance (O&M) divisions had serious concerns about
the toxicity effects of hydrazine on its workers. These
problems have led the management of many steam-
generating plants to seek safer-to-use alternative oxygen
scavengers.
© 2018 by Waesseri GmbH. All rights reserved.
Carbohydrazide vs Hydrazine: A Comparative Study
ABSTRACT
Hydrazine has been extensively used by the Saline Water Conversion Corporation (SWCC) in high-pressure boilers as
an effective oxygen scavenger for the last several decades. However, due to its toxicity there have been serious
thoughts of replacing it with a safer and more effective alternative.
Carbohydrazide, which is marketed under different trade names, was believed to be a good alternative to hydrazine
that provides all of the additional benefits desired of an alternative oxygen scavenger of being safe to handle but
without the deleterious impact on the cycle chemistry.
Trial tests with carbohydrazide on one of Al-Jubail Power Plant's boilers provided evidence that it is a good alternative
to hydrazine. After two weeks of optimization, it was found that maintaining residual hydrazine in the range of
30–40 µg · kg–1 in feedwater (economizer inlet) was an appropriate method of controlling the dose rate of carbo -
hydrazide and hence provided the optimum conditions for passivating the boiler. Accordingly, a dosing rate of
0.7 mg · kg–1 of carbohydrazide was found satisfactory for running the boiler smoothly.
This paper is a summary of the initial trials performed 12 years ago and serves as an introduction to a second article
which will be published later this year in this journal. During the past 12 years, SWCC has been using carbohydrazide
in all of its 8 plants. SWCC has done some studies with different brands and with 6–12 % carbohydrazide used in the
steam cycle as well as during lay-up – this experience will be presented in the next paper.
Mohammed Mahmoodur Rahman, Saad Abdullah Al-Sulami, and Fahad A. Almauili
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PowerPlant Chemistry 2018, 20(1)34
Author's Copy
Carbohydrazide vs Hydrazine: A Comparative Study
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PowerPlant Chemistry 2018, 20(1) 35
Carbohydrazide is reported, under laboratory conditions,
to be more effective than hydrazine in removing oxygen at
all temperatures [10–14]. Carbohydrazide is thermally sta-
ble up to 135 °C and reacts rapidly with oxygen according
to the following reaction (Eq. (1)) at temperatures < 135 °C:
(H2N-NH)2CO + 2O22N2+ 3H2O + CO2(1)
When the temperature exceeds 135 °C, it hydrolyzes to
hydrazine and carbon dioxide (Eqs. 2 and 3):
(H2N-NH)2CO + H2O 2N2H4+ CO2(2)
2N2H4+ 2O24H2O + 2N2(3)
Above 200 °C, it decomposes to ammonia, nitrogen and
carbon dioxide [23–24]:
(H2N-HN)2CO + H2O 2NH3+ N2+ H2+ CO2(4)
It is noted that carbon dioxide is a byproduct of both the
carbohydrazide-oxygen reaction and the subsequent
reversion to hydrazine. At typical application levels of
carbohydrazide, the CO2addition rate was found to be
< 25 µg · kg–1, which is considered to be an amount that
has no major effect on cycle chemistry. In one of the case
studies, in a unit operated with hydrazine, the concentra-
tion of iron at the deaerator and economizer inlet was 9
and 10 µg · kg–1, respectively. Six months after the intro-
duction of carbohydrazide, the iron levels dropped to
about 2 µg · kg–1 at both sample points. The copper con-
centration was also reduced from 7 and 17 µg · kg–1 to
4 and 2 µg · kg–1, respectively. The final dosage of carbo-
hydrazide needed for the ultimate system maintenance
was less than 50 % of the total required at the start-up of
the programme.
Carbohydrazide reacts with iron (Eq. (1)) and copper
(Eq. (2)) oxides to form protective passive oxides:
12Fe2O3+ (NH2-NH)2CO 8Fe3O4+ 3H2O + 2N2+ CO2
(5)
8CuO + (NH2-NH)2CO 4Cu2O + 3H2O + 2N2+ CO2(6)
When applied to the end of the utility cycle, it has the abil-
ity to substantially lower corrosion rates both through
improved oxygen scavenging and through surface chem-
istry reactions that encourage the formation of a highly
protective film [15]. The combined oxygen scavenging-
surface passivation impact was found to be appreciably
better than with hydrazine [16,17].
EXPERIMENTAL
Two boilers (No. 81 and No. 82) of Phase–II at the Al-Jubail
plant, which produce high-pressure steam that drives two
turbines, each with a capacity of 130 MW, were selected
for the trial tests in consultation with the chemical manu-
facturing company.
Item Boiler Material, ASME Code Number
Drum Carbon steel (SA-299)
Superheater Carbon steel. Seamless steel pipes (AS-210)
Primary superheater inlet SA-106-C
Primary superheater outlet SA-335-P12
Secondary superheater inlet SA-106-C
Secondary superheater outlet SA-335-P12
De-superheater inlet SA-335-P12
De-superheater outlet SA-106-C
SCW steam cold wall SA-210-A1
Economizer SA-210-A1
Water tubes (upper / lower) (front / rear and division wall) SA-106-C
HP heater Cu-Ni 70/30
Brine heater Cu-Ni-Fe-Mn 66/30/2/2
Dump condenser Cu-Ni 70/30
Table 1:
Boiler materials.
Author's Copy
Research Objectives
1. To evaluate the suitability and efficiency of carbo -
hydrazide as an alternative oxygen scavenger to
hydrazine in the high-pressure boiler.
2. To determine the consequences of its degradation by-
products on a boiler system.
3. To evaluate the ability of the carbohydrazide to form
and maintain an oxide film in the boiler.
4. To evaluate whether it produces any negative effects on
the efficiency of the boiler.
Boiler material specifications are given in Table 1. Boiler
No. 81 was run with carbohydrazide and Boiler No. 82
with hydrazine. Both these boilers are pressurized box
type water tube boilers. The maximum continuous rating
(MCR) of steam is 710 t per hour. The capacity of the
boiler drum when filled is 150.5 t and along with the super-
heater the total capacity is 189.5 t.
However the operational level is 121 t. The boiler outlet
steam temperature is 523 °C at a pressure of 100 bar. The
feedwater comprising condensed steam plus make-up
water is first passed through the deaerator at a pressure of
5 bar and a temperature of 156 °C. After the deaerator, the
feedwater is dosed with the oxygen scavenger and heated
at two different HP heaters, each at a pressure of 103 bar
and temperatures ranging between 160 and 233 °C. From
the HP heaters it is sent to the economizer at a pressure of
102 bar and the temperature is raised to 295 °C. At about
100 bar and at a temperature of 310 °C it is passed into
the boiler drum. Coordinated phosphate treatment is done
here for pH adjustment. From the boiler drum it is passed
into the superheater, where its temperature is raised to
515 °C at 95 bar pressure. The superheated steam at a
temperature of 515 °C and a pressure of 95 bar goes to
the turbine. The steam leaving the turbine at a pressure of
1.4 bar is sent to heat the recycled brine of the desalina-
tion plants (Figure 1).
The criteria for evaluation were set in consultation with the
chemical supplier. The technical assistance was provided
by the chemical supplier to obtain best performance. All
boiler chemistry limits and test conditions were main-
tained in both the boilers (Tables 2 and 3). The pH was
maintained within a range of 8.2 to 8.5 in the make-up
water using morpholine. Original dosage requirements
PPCHEM
PowerPlant Chemistry 2018, 20(1)36
Figure 1:
Boiler water cycle and sampling points.
Dump
condenser
Turbine
Deaerator
Phosphate
dosing
Demineralized
water pump
(make-up water)
12
HP heater
Boiler water
(boiler blowdown)
sampling point
Feedwater
sampling point
Economizer
Superheater Hydrazine
dosing
Amine
dosing
Brine heater
(desalination plant)
Brine heater
condensate
sampling point
Make-up water
sampling point
Saturated steam
sampling point
Polishing
system
Carbohydrazide vs Hydrazine: A Comparative Study
Author's Copy
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PowerPlant Chemistry 2018, 20(1) 37
were specified by the chemical supplier as 1.5 mg · kg–1
with a residual of 0.5–1.2 mg · kg–1 in the boiler feedwater.
Baseline data using hydrazine was developed over a
period of 4 weeks. This data consisted of iron and copper
concentrations in the economizer inlet (feedwater) sample
as well as pH, ammonia, specific conductivity and dis-
solved oxygen. The chemicals were fed at the deaerator
outlet.
Parameters/Samples Brine Heater Deaerator Feedwater Boiler Saturated
Condensate Outlet Blowdown Steam
pH 8.5–9.2 8.7–9.2 9–9.8 8.7–9.2
Conductivity [µS · cm–1]<3 <3 <50 <3
Conductivity after cation [µS · cm–1]<0.5 < 0.5
exchange (CACE)
Copper [µg · kg–1]<5 <5 <20
Ammonia [mg · kg–1]<0.3 < 0.3 < 0.3
Iron [µg · kg–1]<10 < 10 < 50
Dissolved oxygen [µg · kg–1]<20 < 10 0 or < 7
Hydrazine [µg · kg–1] 10–20
Silica [µg · kg–1]<20 < 20 < 20
Sodium [µg · kg–1]<10 < 10 < 10
Chloride [mg · kg–1]<0.01 < 0.05 < 0.5 < 0.05
Phosphate [mg · kg–1] 5–10
P-Alkalinity [mg · kg–1]<5
M-Alkalinity [mg · kg–1]<15
Table 2:
Chemical parameter limits for normal operation.
Sample No. Equipment Capacity Pressure Temperature Flow
[bar] [°C]
1 Condensate 9.5–9.8 99–121
2 Deaerator 86 m35 156 700 m3per hour
3 Deaerator tower 25 m3
4 Boiler feed pump 900 m3103 141 697 m3per hour
5 HP heater 1 103 160–195 697 m3per hour
6 HP heater 2 103 195–233 697 m3per hour
7 Economizer 102 230–295 700 m3per hour
8 Boiler 121 m3104 310 700 m3per hour
9 Superheater 39 m395 515 700 m3per hour
10 Hydrazine tank pump 560 L 150 50 L per hour
11 Phosphate tank pump 560 L 150 50 L per hour
Table 3:
Test conditions.
Carbohydrazide vs Hydrazine: A Comparative Study
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38 PowerPlant Chemistry 2018, 20(1)
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ANALYTICAL PARAMETERS AND PROCEDURES
Boiler Water Chemistry
The following parameters for boiler water chemistry were
determined: pH, ammonia, copper, dissolved oxygen,
specific conductivity and conductivity after cation
exchange (CACE), residual hydrazine (represented as car-
bohydrazide), iron and phosphate at the following sam-
pling points:
(a) Feedwater (economizer inlet) (FW),
(b) Boiler blowdown (boiler water) (BBD),
(c) Saturated steam (SS),
(d) Brine heater condensate (BHC),
(e) Deaerator outlet (DAO).
Boiler Operation Parameters
Mass flow, temperature and pressure were monitored in
order to evaluate the boiler thermal efficiency.
Corrosion Monitoring
Corrosion coupons were installed with the help of plant
personnel in the following locations and photos were
taken:
(a) Boiler drum: Three coupons of carbon steel were
placed on the waterside and three coupons on the
steamside.
(b) HP heaters: Three coupons of copper-nickel 70/30
and three coupons of carbon steel were placed.
The coupons were withdrawn during the boiler shutdown
for physical examination and evaluated for corrosion rate
by weight loss.
Boiler Shutdown Inspection
Internal inspection of the boiler was carried out at the end
of testing. Besides visual checks and photographic docu-
mentation, chemical analysis of several deposit samples
was carried out.
RESULTS AND DISCUSSION
Boiler Chemistry
Figure 2 represents average values for the pH determined
in FW, BBD, SS, BHC and DAO in comparison to the
results obtained with hydrazine as a baseline and the tests
carried out with carbohydrazide. The values for both
hydrazine and carbohydrazide were found to be main-
tained in the range of 8.6 to 9.0 for BHC, FW, SS and DAO
whereas for BBD it was in the range of 9.0 to 10.
Chemical feed rates for hydrazine were established to
maintain hydrazine residual around 20 µg · kg–1 in the
feedwater (Figure 3). Ammonia concentration (Figure 4)
and specific conductivity (Figure 5) were also found to be
within the limits in the range of 0.12–0.3 µg · kg–1 and
1.8–2.8 µS · cm–1, respectively.
At the start with the recommended dosage of 1.5 mg· kg–1
of carbohydrazide, high concentrations of ammonia
(Figure 4) and copper (Figure 6) were recorded and the
determination of carbohydrazide in the feedwater was
observed to give inconsistent values. The dose rate was
later reduced in consultation with the chemical supplier
from 1.5 mg · kg–1 to 0.7 mg · kg–1 until the parameters
(copper and ammonia) were maintained within the normal
range and stabilized.
The inconsistency observed in the concentration of resid-
ual carbohydrazide in the feedwater (economizer inlet)
was attributed to the high temperature of the feedwater
(235 °C) because at temperatures above 150 °C carbo -
hydrazide hydrolyzes to hydrazine. Since carbohydrazide
is hydrolyzed to hydrazine above 150 °C, it was decided
to monitor carbohydrazide in the feedwater by monitoring
residual hydrazine and to maintain the hydrazine at
30–40 µg · kg–1.
It was observed that the high concentrations of ammonia
and copper were due to excess dosing of carbohydrazide.
The recommended dose rate by the chemical supplier of
1.5 mg · kg–1, was found to be very high. The dose rate
was reduced to 0.7 mg · kg–1 by monitoring carbo -
hydrazide as equivalent to 30–40 µg · kg–1 of residual
hydrazine in the feedwater. All the key parameters (ammo-
nia, specific conductivity, pH and phosphate) were found
to be within the baseline limits (Figures 2, 4 and 5).
With hydrazine, the average concentrations for iron
(Figure 7) and copper (Figure 6) in the feedwater were
found to be 8 µg · kg–1 and 3 µg · kg–1, respectively, and in
the boiler water they were found to be 19 µg · kg–1 and
6 µg · kg–1, respectively, whereas with carbohydrazide
dosing, the average concentrations for iron and copper in
the feedwater were found to be 2 µg · kg–1 and 3 µg · kg–1,
respectively, and in the boiler water they were found to be
17 µg · kg–1 and 4 µg · kg–1, respectively. This showed a
reduction in iron levels in the feedwater by 75 % whereas
copper was found to be maintained at the baseline value.
In the boiler water (drum) the reductions in iron and copper
were found to be 10 % and 33 %, respectively.
The average dissolved oxygen with both hydrazine and
carbohydrazide in the DAO was found to be 7 µg · kg–1,
whereas in the BHC it was found to be high, at an average
Carbohydrazide vs Hydrazine: A Comparative Study
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39PowerPlant Chemistry 2018, 20(1)
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Figure 2:
Average pH values for hydrazine and carbohydrazide in different streams of the boiler.
9.6
9.4
9.2
9.0
8.8
8.6
8.4
8.2
FW pH
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Date [m/d/y]
10.7
10.2
9.7
9.2
8.7
8.2
BBD pH
9.4
9.2
9.0
8.8
8.6
8.4
8.2
BHC pH
9.4
9.2
9.0
8.8
8.6
8.4
8.2
SS pH
9.4
9.2
9.0
8.8
8.6
8.4
8.2
DAO pH
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Date [m/d/y]
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Date [m/d/y]
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Date [m/d/y]
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Date [m/d/y]
Carbohydrazide Hydrazine Limit
of 87 µg · kg–1 (Figure 8). This was attributed to air inleak-
age. CACE in the BHC and SS was found to be
0.1 µS · cm–1 and the phosphate determined in the boiler
water was found to be maintained in the range of 5 to
7 mg · kg–1.
The boiler thermal efficiency was maintained within the
normally experienced range.
Carbohydrazide vs Hydrazine: A Comparative Study
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40 PowerPlant Chemistry 2018, 20(1)
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Figure 3:
Average values for residual hydrazine and carbohydrazide in different streams of the boiler.
250
200
150
100
50
0
FW Carbohydrazide Concentration
[µg kg ]
·–1
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Date [m/d/y]
30
25
20
15
10
5
0
250
200
150
100
50
0
BBD
[µg kg ]
Carbohydrazide Concentration
·–1
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Date [m/d/y]
BBD Hydrazine [µg kg ]
·–1
Concentration
25
20
15
10
5
0
FW Hydrazine [µg kg ]
·–1
Concentration
Carbohydrazide Hydrazine Limit
Figure 4:
Average ammonia values for hydrazine and carbohydrazide in different streams of the boiler.
1.2
1.0
0.8
0.6
0.4
0.2
0
FW Ammonia Concentration [mg kg ]
·–1
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Date [m/d/y]
1.0
0.8
0.6
0.4
0.2
0
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Date [m/d/y]
SS Ammonia [mg kg ]
·–1
Concentration
Carbohydrazide Hydrazine Limit
Carbohydrazide vs Hydrazine: A Comparative Study
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41PowerPlant Chemistry 2018, 20(1)
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Figure 5:
Average specific conductivity values for hydrazine and carbohydrazide in different streams of the boiler.
6
5
4
3
2
1
0
BHC Conductivity [µS cm ]
·–1
6
5
4
3
2
1
0
FW Conductivity [µS cm ]
·–1
SS Conductivity [µS cm ]
·–1
6
5
4
3
2
1
0
DAO Conductivity [µS cm ]
·–1
5
4
3
2
1
0
BBD Conductivity [µS cm ]
·–1
60
50
40
30
20
10
0
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Date [m/d/y]
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Date [m/d/y]
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Date [m/d/y]
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Date [m/d/y]
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Date [m/d/y]
Carbohydrazide Hydrazine Limit
Carbohydrazide vs Hydrazine: A Comparative Study
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42 PowerPlant Chemistry 2018, 20(1)
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Corrosion Studies
The exposed coupons were visually examined. A uniform
and non-porous oxide film was found to be adhered to the
coupons indicating the protective nature of the films. The
corrosion rate of 1.12 µm per year determined for the
carbon steel coupons fixed in the drum on the waterside
with hydrazine dosing indicates extremely low corrosion.
Although a total of 12 coupons of carbon steel and
cupronickel 70/30 were fixed, only two of carbon steel
(from the boiler drum waterside) could be retrieved for reli-
able corrosion rate determination. The rest were damaged
during removal from the unit.
The corrosion rates determined with carbohydrazide dos-
ing for carbon steel coupons fixed in the drum on the
water- and steamside were 9.75 µm per year and
11.28 µm per year, respectively, whereas those deter-
mined for carbon steel and cupronickel 70/30 in the HP
heaters were 6.38 µm per year and 3.25 µm per year,
respectively. The corrosion rates of the material appear to
be low and the effect of corrosion appears to be insignif -
icant.
Physical Examination of Coupons
Physical examination of the carbon steel coupons treated
with hydrazine retrieved from the drum (water- and steam-
side, Figure 9) showed dark grey oxide scales and
appeared to be protective except on some coupons
where scales had been removed due to mechanical dam-
age. The cupronickel coupons removed from the HP
heaters were found to have dark grey or brownish red
scales (Figure 10). The scales appeared to be uniform and
adherent but were slightly damaged from handling. With
carbohydrazide dosing, uniform, non-porous, dark-grey
scales adhered on the carbon steel coupons retrieved
from both the water- and steamsides of the drum were
observed (Figures 11 and 12). The cupronickel coupons
Figure 6:
Average copper values for hydrazine and carbohydrazide in different streams of the boiler.
40
35
30
25
20
15
10
5
0
FW Copper Concentration [µg kg ]
·–1
50
45
40
35
30
25
20
15
10
5
0
5/17/05 6/17/05 7/17/05 8/17/05 9/17/05
Date [m/d/y]
BBD Copper [µg kg ]
·–1
Concentration
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Date [m/d/y]
Carbohydrazide Hydrazine Limit
Carbohydrazide vs Hydrazine: A Comparative Study
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43PowerPlant Chemistry 2018, 20(1)
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fixed at the HP heaters also showed uniform dark-grey
scales (Figures 13 and 14). The dark-grey Fe3O4and
cuprous oxide scales which developed on the coupons in
general appeared to be protective.
Boiler Inspection and Deposits Analysis
Boiler No. 82 selected for the hydrazine baseline was
inspected visually and photographically documented. The
inside of the boiler drum was shown to be coated with a
dark-grey uniform thin layer of oxide film and the HP
heaters (Figure 15) showed a brownish-red coating.
The deposits collected from the boiler drum (treated with
hydrazine) during the shutdown were subjected to chemi-
cal analysis both by energy dispersive X-ray (EDX) and
inductive coupled plasma (ICP). The EDX profile showed
predominantly iron with moderate concentrations of cop-
per and nickel whereas the ICP analysis showed the
deposits to be rich in iron (44.4 %) with a relatively high
concentration of copper (27.2 %) and with significant
amounts of nickel (8.0 %). The presence of high concen-
trations of iron and copper shows carryover of corrosion
products from the carbon steel tubes of the boiler and
copper alloy heat exchanger tubes.
Boiler No. 81 selected for carbohydrazide testing was
found to be uniformly coated with dark grey deposits
(Figures 16 and 17). Deposits analysis showed that the
composition was similar to that treated with hydrazine
(Table 4). The chemical analysis of the deposits showed
that iron was predominant (49.6 %) along with significant
amounts of copper (26.2 %) and nickel (4.7 %). The pres-
ence of high concentrations of copper and nickel shows
carryover of corrosion products from the copper alloy heat
exchanger tubes.
Figure 7:
Average iron values for hydrazine and carbohydrazide in different streams of the boiler.
25
20
15
10
5
0
FW Iron [µg kg ]
·–1
Concentration
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Date [m/d/y]
60
50
40
30
20
10
0
BBD Iron [µg kg ]
·–1
Concentration
5/17/05 5/31/05 6/14/05 6/28/05 7/12/05 7/26/05 8/9/05 8/23/05 9/6/05 9/20/05 10/4/05
Date [m/d/y]
Carbohydrazide Hydrazine Limit
Carbohydrazide vs Hydrazine: A Comparative Study
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44 PowerPlant Chemistry 2018, 20(1)
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Figure 8:
Average dissolved oxygen values for hydrazine and carbohydrazide in different streams of the boiler.
14
12
10
8
6
4
2
0
DAO Dissolved Oxygen [µg kg ]
·
–1
5/17/05 5/31/05 6/14/05 6/28/05 7/12/05 7/26/05 8/9/05 8/23/05 9/6/05 9/20/05 10/4/05
Date [m/d/y]
250
200
150
100
50
0
BHC Dissolved Oxygen [µg kg ]
·
–1
5/17/05 5/31/05 6/14/05 6/28/05 7/12/05 7/26/05 8/9/05 8/23/05 9/6/05 9/20/05 10/4/05
Date [m/d/y]
Carbohydrazide Hydrazine Limit
Figure 9:
Photographs showing carbon steel coupons after exposure in water drum (water- and steamside) under hydrazine dosing in Boiler No. 82.
Figure 10:
Photographs showing carbon steel and cupronickel 70/30 coupons after exposure in HP heater under hydrazine dosing in Boiler No. 82.
Carbohydrazide vs Hydrazine: A Comparative Study
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45PowerPlant Chemistry 2018, 20(1)
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Figure 11:
Photographs showing: (a) inside drum and coupons and (b) water box side of HP heater and coupons of Boiler No. 82 before
hydrazine dosing.
Figure 12:
Photographs showing carbon steel coupons after exposure in water drum (waterside) under carbohydrazide dosing in Boiler No. 81.
Figure 13:
Photographs showing carbon steel coupons after exposure in water drum (steamside) under carbohydrazide dosing in Boiler No. 81.
Carbohydrazide vs Hydrazine: A Comparative Study
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46 PowerPlant Chemistry 2018, 20(1)
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Figure 14:
Photographs showing carbon steel coupons after exposure in HP heater under carbohydrazide dosing in Boiler No. 81.
Figure 15:
Photographs showing cupronickel 70/30 coupons after exposure in HP heater under carbohydrazide dosing in Boiler No. 81.
Figure 16:
Photographs showing Boiler No. 81: inside drum and the coupons (a) before carbohydrazide dosing, and (b) after carbohydrazide
dosing.
Carbohydrazide vs Hydrazine: A Comparative Study
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47PowerPlant Chemistry 2018, 20(1)
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CONCLUSIONS
1. The results indicated the suitability and efficiency of
carbohydrazide as an alternative to hydrazine in
SWCC high-pressure boilers provided the concentra-
tion of residual hydrazine (a decomposition by-product
of carbohydrazide) is maintained at levels between 30
and 40 µg · kg–1 in the feedwater.
2. No harmful degradation by-products were found.
3. Carbohydrazide was found to be a good oxygen scav-
enger at a concentration of 0.7 mg · kg–1.
4. An optimized dose rate has resulted in maintaining the
boiler chemistry within design limits.
5. Iron levels measured at the economizer inlet (boiler
feedwater) were reduced by 75 % whereas copper was
found to be maintained at the baseline value. In the
boiler water (drum) the reductions in iron and copper
were 10 % and 33 %, respectively.
6. The corrosion rates indicated very little or negligible
corrosion due to either hydrazine or carbohydrazide.
However, hydrazine showed much lower rates com-
pared to carbohydrazide.
7. Physical examination of the coupons revealed that
both hydrazine and carbohydrazide help in the devel-
opment of uniform, non-porous film adhered to the
metal, indicating the protective nature of the film.
Figure 17:
Photographs showing: (a) water box side of HP heater and the coupons of Boiler No. 81 before the test, and (b) water box side of HP
heater and the coupons of Boiler No. 81 after the test.
Sample No. Parameter Boiler No. 81 (Carbohydrazide) Boiler No. 82 (Hydrazine)
Mass Fraction [%] Mass Fraction [%]
1 Al < 0.1 < 0.1
2 Ca < 0.1 < 0.1
3 Mo < 0.1 < 0.1
4 Cr 0.1 < 0.1
5 Mn 0.3 0.3
6 Ni 4.7 8.0
7 Cu 26.2 27.2
8 Fe 49.6 44.4
9 Si (soluble) < 0.1 < 0.1
Table 4:
Chemical analysis of deposits from drum of boilers No. 81, and No. 82.
Carbohydrazide vs Hydrazine: A Comparative Study
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48 PowerPlant Chemistry 2018, 20(1)
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REFERENCES
[1] Technical Guidance Document – Volatile Treatments
for the Steam-Water Circuits of Fossil and Combined
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[2] Technical Guidance Document – Phosphate and
NaOH Treatments for the Steam-Water Circuits of
Drum Boilers of Fossil and Combined Cycle/HRSG
Power Plants, 2015. International Association for the
Properties of Water and Steam, IAPWS TGD3-
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[3] ASME, Boiler and Pressure Vessel Code, Section VII,
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THE AUTHORS
Mohammed Mahmoodur Rahman (Ph.D., Chemistry,
University of Poona, India) has been active in the field of
desalination, environmental, power plant, and solid state
chemistry for the last 22 years. His early career in India
focused on synthesis and properties of magnetic materi-
als. After relocating to Saudi Arabia, he worked exten-
sively with water desalination, boiler water chemistry,
environmental chemistry and troubleshooting for reverse
osmosis pretreatment applications. Dr. M. Mahmoodur
Rahman is currently working as a researcher at the
Desalination Technologies Research Institute (DTRI) at the
Saline Water Conversion Corporation (SWCC), Saudi
Arabia. He has several technical and scientific publica-
tions in national and international journals in desalination,
environmental, and boiler water chemistry. He has pre-
sented a number of research papers at local and interna-
tional conferences. He is a member of the International
Desalination Association (IDA).
Saad Abdullah Al-Sulami (B.Sc., Industrial Chemistry,
King Fahd University of Petroleum and Minerals (KFUPM),
Saudi Arabia) has been employed at the SWCC for more
than two decades. He currently holds the position of head
of the chemistry department at DTRI and is a desalination
specialist. He is a member of IDA and the Saudi Council of
Engineers. As a chemical specialist, he has been involved
in desalination research and development for more than
20 years, leading research efforts in scale inhibitor perfor-
mance, pretreatment program evaluation of seawater, and
water transmission pipelines. He has many publications in
scientific journals and has presented his research work at
many scientific conferences.
Carbohydrazide vs Hydrazine: A Comparative Study
Author's Copy
49PowerPlant Chemistry 2018, 20(1)
PPCHEM
Fahad A. Almauili (B.S., Chemical Engineering, King
Saud University, Saudi Arabia, M.S., Advanced
Engineering Materials, University of Manchester, United
Kingdom) has been employed with SWCC for more than
14 years and was recently promoted to the position of
specialist corrosion engineer. He has been actively
involved in corrosion research relevant to desalination,
power plants, and water transmission systems. He is a
member of IDA and the Saudi Council of Engineers
and has many publications in scientific journals and con-
ferences.
CONTACT
Mohammed Mahmoodur Rahman
Saline Water Conversion Corporation
Desalination Technologies Research Institute
PO Box 8328
Al-Jubail 31951
Kingdom of Saudi Arabia
E-mail: m1a1609@swcc.gov.sa
Carbohydrazide vs Hydrazine: A Comparative Study / Event
Author's Copy
Article
The surface condenser in the steam turbine plays an essential role during the condensation process. Failure of surface condenser tubes is a critical factor for its efficiency and lifetime. This paper presents the failure of a surface condenser's admiralty brass tubes from a petrochemical plant in Indonesia after four years out of twenty years of expected lifetime. Eddy Current inspection results show some of the leaks were in the condensing zone. The characteristics of ammonia corrosion were found after visual and SEM examinations. Examination using stereo and metallurgical microscopes showed that the tubes' external surface experienced corrosion, grooving attack, and significant wall thinning. SEM observation at the edge of the baffle revealed the preferential attack at the alloy's grain boundaries. Water quality analysis indicated high ammonia concentration because the excess amount of Elimin-Ox oxygen scavenger in the water can produce ammonia that corroded the tubes, leading to leakage and failure.
Article
The efficiency of a range of hydrazine alternatives (carbohydrazide, diethyl-hydroxylamine, erythorbic acid and 2-butanone oxime) as oxygen scavengers and their interaction with carbon steel in simulated PWR steam generator inlet conditions are quantitatively compared. Kinetic parameters of oxygen reaction are estimated for the first time in such conditions using both an oxygen and a redox sensor. Electrochemical impedance measurements are performed to investigate the effect of studied alternatives on carbon steel corrosion. Using a quantitative interpretation of the impedance data by the Mixed-Conduction Model, the influence of hydrazine and its alternatives on charge transfer reactions at the oxide/solution interface and film growth/dissolution processes are discriminated. Conclusions are drawn on the comparative reaction rates of hydrazine alternatives with respect to oxygen consumption and steel passivation.
Article
Dickinson, et al investigated the reaction rate between hydrazine and oxygen. They concluded the overall reaction was first order. Their data were reanalyzed. The results indicate the reaction is first order with respect to oxygen and one-half order with respect to hydrazine.
Boiler and Pressure Vessel Code, Section VII
ASME, Boiler and Pressure Vessel Code, Section VII, 1989. American Society of Mechanical Engineers, New York, NY, U.S.A., 97.
Engineers' Society of Western Pennsylvania
  • L L Schneider
  • D C Hutchens
Schneider, L. L., Hutchens, D. C., Proc., Inter national Water Conference, 1986 (Pittsburgh, PA, U.S.A.). Engineers' Society of Western Pennsylvania, Pittsburgh, PA, U.S.A., IWC-86-21.
Materials Performance
  • V Andriés
  • D Couturier
Andriés, V., Couturier, D., Materials Performance 2000, 39(7), 58.
  • A P Akol'zin
  • V G Klochkova
  • A E Balabanov
Akol'zin A. P., Klochkova V. G., Balabanov A. E., Thermal Engineering 1988, 35(8), 462.
) Engineers' Society of Western Pennsylvania
  • D Bloom
  • L R Gess
Bloom, D., Gess, L. R., Proc., International Water Conference, 1980 (Pittsburgh, PA, U.S.A.) Engineers' Society of Western Pennsylvania, Pittsburgh, PA, U.S.A., IWC-80-47.
National Association of Corrosion Engineers
  • P A Reardon
  • W E Bernahl
Reardon, P. A., Bernahl, W. E., Proc., CORRO-SION/87, 1987 (San Francisco, CA, U.S.A.). National Association of Corrosion Engineers, Houston, TX, U.S.A., Paper No. 87438.
Applied Thermal Engineering
  • S M V Vasile-Pafili
  • J G Bartzis
Vasile-Pafili, S. M. V., Bartzis, J. G., Applied Thermal Engineering 2010, 30(10), 1269.