Gezira j. of Eng. & applied. Sci.  12-(1): 16-30 (2017)

 

Effect of Boiler Feed Water Quality in Textile and Other Industries

Mutasim Abdalla Ahmed1 Musa Eltayib Babiker2

1Faculty of Textile, University of Gezira.

2 Faculty of Textile,University of Gezira

 

ABSTRACT

  Chemical processing of textile is one of the major streams in textile industry in which many activities are included such as, preparation, dyeing and finishing due to its importance for value addition. This study aims to assess the constituents of boiler feed water for different industries. The study was limited to, Blue Nile Textile Company, Gematex Textile Company, Kenana Sugar Company and Khartoum Refinery Company. Boiler feed water samples from each industry were collected using standard sampling techniques at different intervals of times, before and after treatment. Various analytical and instrumental test methods were carried out, using UV- visible and atomic absorption spectrophotometers, flame photometers, turbidity and pH meters. Results of pH, EC, TDS, hardness, anions and cations were determined and compared to the standard ASME guidelines. It is found that all water samples of the four industries constitute various anions and cations with varying degrees. Gematex company showed the highest values of total hardness, calcium ions, carbonates and bicarbonates ions comparative to the other industries, and mostly exceeding the ASME Guidelines. K.S.C. and K.R.C. showed lower levels of impurities because, their boiler feed water was relatively better treated and conditioned, although some results of their tested water samples exceeded the ASME Guidelines. High levels of total hardness, in the boiler water may cause problems concerning boiler performance. pH levels of all companies were found to be below the specified standard guidelines, therefore dealkalization should  be carried out to avoid corrosion. The four companies need proper treatments to reduce the levels of anions and cations within the recommended ASME Guidelines. A reliable water treatment unit is highly recommended for every industry adopting boilers for steam generation. A reverse osmosis system is to be added to the line of treatment as it removes physically anions and cations. Micro processing indicators that can digitally display chemical measurements of some properties of the treated water in – line with the treatment process is also recommended. Application of a genuine, stringent legal testing, training and certification systems may be imposed by the ministry of industry and inspect periodically the conditions of the boilers of the industry in the country.

 

Key Words: Boiler – Steam - Industry - Treatment - Textile - hardness

 

INTRODUCTION

  Textile industry is a complex industry due to including various mills such as spinning, weaving, knitting, pretreatment, dyeing, finishing and garments. Steaming is one of the most important processes in the textile wet processing. Wet processing engineering is one of the major streams in textile industry which refers to textile chemical engineering in which many activities are included under this name. Chemical processing of textile, such as preparation, dyeing and finishing is important for its value addition fashion and function. However, these processes are water, energy and chemical intensive. (Kartic, et al,) (2014).

 Wet textile processing industry, sugar industry and petroleum refinery processes require significant quantities of water and heat energy. Heat in the form of steam, which is generated by boilers, is widely used for unit operations and chemical processes. For textile chemical processing steam is used for fixation of chemicals, dyestuff, finishing agents, and for drying of textile materials, Mishra,(2010).    

A boiler is a closed vessel in which water under pressure is transformed into steam by the application of heat. In the boiler furnace, the chemical energy in the fuel is converted into heat, and it is the function of the boiler to transfer this heat to the contained water in the most efficient manner. A boiler should also be designed to generate high quality steam for plant use, and absorb the maximum amount of heat released in the process of combustion. This heat is transferred to the boiler water through radiation, conduction and convection. The relative percentage of each is dependent upon the type of boiler, the designed heat transfer surface and the fuels, (Mallikarjuna, et al, 2014).

 

The principal types of boilers:

 

There are basically two types of boilers: 

Fire tube boilers - Products of combustion pass through the tubes, which are surrounded by water.

              Fig. (1):   Work of steam engines (fire -tube boiler)

               Source:-http://en.wikipedia.org/wiki

2. Water tube boilers - Products of combustion pass around the tubes containing water. The tubes are interconnected to common channels or headers and eventually to a steam outlet for distribution to the plant system.

    Fig. (2): Schematic diagram of a marine-type water tube boiler

   Source: https://en.wikipedia.org/wiki

The boiler system is composed of: feed water system, steam system and fuel system. The feed water system provides water to the boiler and regulates it automatically to meet the steam demand. Steam is directed through a piping system to the point of use. Throughout the system, steam pressure is regulated using valves and checked with steam pressure gauges. The fuel system includes all equipment used to provide fuel to generate the necessary heat. (Gupta, et al, 2012).

 The boiler feed water constituents unless carefully treated, monitored, and conditioned will impose serious problems concerning the performance of the steam boiler and the cost of production as well, Mishra, (2010).

Water absorbs more heat for a given temperature rise than any other common inorganic substance. It expands 1600 times as it evaporates to steam at atmospheric pressure. The steam is capable of carrying large quantities of heat. These unique properties of water make it an ideal raw material for heating and power generation processes, (Babiker, 2016).

  All natural waters contain varying amounts of impurities, dissolved, suspended matters or dissolved gases. The amount of mineral dissolved in water varies from 30 g/L in sea water to anything from 0.005 to 1500 mg/L in fresh water supplies. Since water impurities cause boiler problems, careful considerations must be given to the quality of the water used for generating steam, (Babcock and Wilcox, 2007).

Completely pure water, although desirable for steam generating system is non-existing. The major problems associated with boiler feed water impurities are: scaling /deposition, corrosion- oxygen attack, and boiler water carryover.  The composition of boiler feed water must be such that the impurities can be concentrated to a reasonable number of times inside the boiler without exceeding the tolerance limits of the particular boiler design. If the feed water does not meet these requirements, it must be pretreated to remove the impurities. Impurities need not to be removed completely in all cases, however, since chemical treatments inside the boiler can effectively and economically counteract them.

Feed water purity is the matter of quality and nature of impurities. Some impurities such as hardness, iron and silica are of more concern than sodium salts. The purity requirement for any feed water depends on how much feed water is used, as well as, what the particular boiler design, pressure, heat transfer, etc. can tolerate, therefore can vary widely. A low pressure fire tube boiler can usually tolerate high feed water hardness with proper treatment while, virtually all impurities must be removed from water used in some model high pressure boilers. Only relatively wide ranges can be given as to maximum levels of alkalis, salts, silica, phosphates, etc. in relation to working pressure. (Babcock and Wilcox, 2007).

Boiler water treatment may be internal or external. Internal treatment is then applied to minimize the potential problems and to avoid any catastrophic failure, regardless of external treatment malfunction, (http://www.gc3.com/Default.aspx).  

Many factors are involved in proper selection of feed water preparation and internal treatment. Principally, these are the requirements of the plant for safe and reliable operation at an economical treating cost. Boiler water treatment is used to control alkalinity, prevent scaling, correct pH, and to control conductivity. The boiler water needs to be alkaline and not acidic, so that it does not ruin the tubes. There can be too much conductivity in the feed water when there are too many dissolved solids. The main objective for treatment and conditioning of boiler water is to exchange heat without scaling, and produce high quality steam, (Sendalbach, 1988).

 External treatment, as the term is applied to water prepared for use as boiler feed water, usually refers to the chemical and mechanical treatments of water source. The goal is to improve the quality of this source prior to its use as boiler feed water, these operations normally includes: Clarification, filtration, softening, dealkalization, demineralization, deaeration, and heating, , (http://www.gc3.com/Default.aspx).

Boiler feed water that contains calcium and magnesium hardness, migratory iron, migratory copper, colloidal silica and other contaminants will form lime scales deposits, which can contribute to the insufficient operation or failure of water-using appliances. Pipes may become clogged with scales that reduce water flow and ultimately requires pipes replacement. Lime scale has been known to increase energy bill by 25%, (Colin, 2002).

Deposition and scale formation in steam generating systems result from the fact that the solubility of the deposit forming salts decreases with increasing temperature and concentration.  The most common constituents are, calcium, magnesium, bicarbonates, carbonates, phosphates, sulfates, silicates, iron. (James, et al, 2015).    

Dissolved oxygen and dissolved carbon dioxide are among the principal causes of corrosion in the boiler and pre-boiler systems. The deposition of these metallic oxides in the boiler is frequently more troublesome than the actual damage caused by the corrosion. Deposition is not only harmful in itself, but it offers an opening for further corrosion mechanisms as well. The best way to start to control pre-boiler corrosion and ultimate deposition in the boiler is to eliminate the contaminants from the feed water such as, oxygen, the impact of trace amounts of contaminants remaining in the feed water, and heat exchange impact (http://www.gc3.com/Default.aspx ).

The boiler feed water constituents unless carefully treated, monitored, and conditioned will impose serious problems such as scaling /deposition, corrosion- oxygen attack, and boiler water carryover, which affect the performance of steam boiler and increase the cost of production. All natural waters contain varying amounts of impurities, dissolved, suspended matters or dissolved gases. Since water impurities cause boiler problems, careful considerations must be given to the quality of water used for generating steam by internal and external treatments. Consequently, this study aims to evaluate the boiler feed water  constituents of four companies and to compare the results with some ASME Guidelines for Water Quality in Modern Industrial Water Tube Boilers.

MATERIALS AND METHODS

This study was conducted at Faculty of Textile and the Faculty of Engineering and Technology, University of Gezira, Water Conservation Corporation (Wad Medani).  

1- Materials:

1.1 Water samples:

The water samples were collected from each of the following locations:

a.            Blue Nile Textile Company, Wad Medani City.

b.           Gematex Textile Company, East Wad Medani.

c.            Kenana Sugar Company.

d.           Khartoum Refinery Company, Khartoum North.

Three samples each of two litres were collected using standard sampling techniques at different intervals of times. The first samples were taken from the tank fed before treatment whereas the second samples were collected after the water being treated.

2- Methods

Various analytical and instrumental test methods were carried out, such as UV- visible and atomic absorption spectrophotometers, flame photometer, turbidity and pH meters.

Standard solutions were prepared and used in the titration and determination of the constituents using different instruments and standard methods. pH, EC, TDS values were determined by microprocessors.

2.1 Total Dissolved Solids (TDS):

Total Dissolved Solids (TDS) was measured by TDS meter each sample was examined for the total dissolved solids using an electrical conductivity meter (model MC-1 Mark V Eit 5003 England), (Method USEPA 160.2).

2.2 pH value:

pH value was measured by digital pH meter (model Hm 20E Japan); using method (J.I.S., L0886, 1978.

 

 

2.3 Electric conductivity (EC):

Electric conductivity (EC) was measured by electric conductivity meter. A measuring set was used with specific conductance cell and it was calibrated with (0.01M) KCl the conductivities of the samples were then determined in (mmhos/cm) (Aranold et al.,1992).

2.4 Determination of hardness:

Permanent hardness was estimated by evaporating 100 ml of water to dryness on a water bath, with a known volume of 0.1 M sodium carbonate solution. The residue was extracted with freshly boiled hot distilled water and filtered. The insoluble calcium carbonate on the filter paper was thoroughly washed. The filterate (containing the permanent hardness) was cooled and titrated with 0.1 M sodium carbonate solution in the presence of methyl orange indicator.

Total hardness was determined using EDTA titrimetric method as described in Vogel, et al, (1978).

2.5 Carbonates and bicarbonates:

To 50 ml of water sample few drops of  phenolphthalein indicator solution or methyl orange indicator were added and the sample was titrated with (0.1 M) HCl until the color changes from red to blue, Aranold et. al.,(1992).

  2.6 Calcium ions (Ca+2):

The method used was according to that described by Aranold et al, (1992).

2.7 Chloride ions :

The instrument used was UV-Spectrometer model-450, Hach Company, Loveland Co . The method used was mercuric thiocynate (method 8113), Hach program 1400 for water and wastewater adapted from Zall, etal, (analytical chemistry, 1956).

2.8 Sulphate ions (SO4-2 ): 

   The instrument used was UV-Spectrometer. The method used was (Sulfa Ver4 method 8051), using power pillows adapted from standard methods for examination of water and wastewater procedure which is equivalent to US, EPA method.

 RESULTS AND DISCUSSION

Some informations were collected from the four industries as shown in table (1).

 

 

 

Table (1): Summary of information collected from the four industries

Industry

Water sample

Source of water

Boiler types

Manu-facturer

Total capacity ton/hr

Year of start

Present condit-ion

Purpose

BBlue Nile Textile Factory

(a)

WWell

FFire- tube

MMulti- pack (England)

 

10

 

11978/

11980

3One boiler is fair

HHeat

GGematex Textile Factory

(b)

WWell

FFire- tube

(-

 

10

11978

2One  boiler is fair

HHeat

KK.S.C

(c)

RRiver

WWater tube

TTakume (Japan)

 

30

11978

Ggood

PPower Generation and Heat

KK.R.C

(d)

RRiver

WWater tube

HHarbin (China)

 

75

 

11999

Vvery good

PPower Generation and Heat

 

 

Results of boiler feed water constituents were determined volumetrically and gravimetrically for each industry. Results were first tabulated in ml titrant according to the method used and then calculated for every ion detected and then compared with some standards such as the American society of mechanical engineering (ASME) as in table (2).

Table (2): ASME Guidelines for Water Quality in Modern Industrial Water Tube Boilers for Reliable Continuous Operation

Drum

Pressure

(psi)

Total dis-solved solids max

(ppm) boiler

Copper (ppmCu)

Total  Hardness

(ppmCaCo3)

Silica

(ppm Sio2)

Total     alkalinity (ppm CaCo3)

Boiler water

Specific

Conductance

(micromhos/cm

0-300

700-3500

0.050

0.300

150

700 - 140

100- 5400

301-450

600-3000

0.025

0.300

90

600 -120

900- 4600

451-600

500-2500

0.020

0.200

40

500 -100

800- 3800

601-750

200- 1000

0.020

0.200

30

200-40

300- 1500

751-900

150- 750

0.015

0.100

20

150-  30

200- 1200

901-1000

125- 625

0.015

0.050

8

125 - 25

200- 1200

1001-1800

100

0.010

0.0

2

0***

150

1801-2350

50

0.010

0.0

1

0***

100

Source: http://nem.org.uk/steam.htm#top

 

Total hardness:

The total hardness was determined for the boiler feed water of every company using the average values of the calculated titrant before treatment and after treatment as in table (3).

Table (3): Total hardness as CaCO3 (ppm) for the water samples of the four industries

Location

Average hardness  (ppm)

Standard specified hardness value

Before treatment

After treatment

< 10 ppm 

B.N.T

313

150

Gematex

364

          159

K.S.C

244

100

K.R.C

180

40

 

The total hardness is an expression of the quantity of calcium carbonate that may deposit while boiling and form scales on pipes and other parts of the boiler. Precipitation of solids will form hard deposits which act as insulators and lower the heat transfer if allowed to adhere to these surfaces. This will definitely lower the performance and efficiency of the boiler. Table (3) shows that Gematex Company shows the highest total hardness among the four companies studied. Nevertheless all the values of the four companies exceed the standard guidelines of the maximum permissible levels which is less than 10 ppm. (w.w.w.com/Boiler water treatment).

pH values:

pH values were determined for the boiler feed water every company using a digital microprocessor. Table (4) shows the values of pH before and after the treatment of the boiler feed water of the four companies.

  Table (4): pH values for the boiler feed water samples of the four industries

Industry

pH

Standard pH guidlines

Before treatment

After treatment

8.5 – 9.5

B.N.T

8.0

8.2.

Gematex

7.8

8.0

K.S.C

6.7

7.5

K.R.C

7.9

8.7

As table (4) shows, the standard specified pH values for boiler feed water should be in the range of (8.5-9.5) as stated by the Bureau of Indian Standard.  K.R.C. is the only one of the four companies within the specified standard (pH=8.7). The other companies where their boilers feed water are tested need dealkalization. Maintaining of pH closer to alkaline will help to maintain a passivation layer which protects the boiler from corrosion attack. Acidic medium in boiler feed water is corrosive and may cause damage to the parts of the boiler and holes in pipes. This phenomenon was noticed in both Gematex and Blue Nile textile factories.

Total dissolved solids:

The total dissolved solids were determined using a micro processing digital device as shown in table (5).

          Table (5): Results of the total dissolve solids for the four companies

Industry

TDS Mg/L

Standard  guidelines TDS

Before treatment

After treatment

Up to 4000

B.N.T

295

198

Gematex

450

355

K.S.C

320

60

K.R.C

115

40

 

Table (5) reveals that the total dissolved solids in the boiler feed water of Gematex textile factory was the highest among the four factories,  while  K.R.C shows the least TDS. It is obvious that the water treatment and conditioning processes carried out lead to a big  decrease of the total dissolved solids values , even though they are still within the  specified standard value of total dissolved solids for boiler feed water as stated  by (Degremont, 1991) which is up to 4000 Mg/L. In other reference, (source: www2 spraxsarco com/re:) gives  the maximum permissible levels of boiler water TDS  is in the range of 1500 -10000 ppm depending on the type of boiler. Higher levels of TDS in boiler feed water may give rise to foaming. The actual dissolved solid concentrations at which foaming may start will vary from boiler to boiler. Conventional shell boilers are normally operated with TDS values in the range of 2000 ppm for larger boilers provided that the:

-                      Boiler operates near its design pressure

-                      Other boiler water conditions are correctly controlled.

 

 

Electrical conductivity (E.C):

The values of the E.C. for the boiler feed water of the four companies were determined using a microprocessor digital device as in table (6) below.

 Table (6): Results of E.C. for the boiler feed water samples of the four companies

Company

E.C. Micro-ohms/cm

Before treatment

After treatment

B.N.T

347

305

Gematex

863

653

K.S.C

425

113

K.R.C

245

80

 

As in table (6) the electrical conductivity E.C. values for the boiler feed water of Gematex company is the highest before treatment, where as those for K.R.C are the lowest. After treatment the same results could be revealed. Very high reduction was detected for K.R.C and K.S.C after treatment due their proper behavior of water treatment and conditioning of their boiler feed water. Since E.C is directly proportional to the amount of dissolved solids in water, and it is an excellent indicator of total dissolved substances (TDS), its presence will lead formation of foaming in the boiler.

Some ions of the boiler feed water samples of the four industries:

  The average values of ml titrant were used to calculate the amount of these ions in ppm. As shown in table (7).

Table (7): Results of some ions (ppm) in boiler feed water of the four companies. 

Anions / cations

B.N Textile

Gematex

K.S.C

K.R.C

STD

84.40

146.00

40.60

15.20

≥ 6.0 

8.7

60.35

61.06

35.0

ــــ

46

222

60

24.4

 ≥ 4.0 

0.00

83.0

60.0

40.0

ــــ

 

Table (7) shows the values of calcium, carbonate and bicarbonate and hence the total hardness concentrations of the boiler feed water samples of Gematex company are the highest among the four companies. Both results may be considered as reasons behind boiler deterioration and deficiency in a comparatively short period.  B.N. Textile company values of these ions are also high and may be one of the reasons behind causing damage to their boilers. K.S.C and K.R.C companies comparatively show lower levels of these ions but even though their values are higher than the standard guidelines specified by the Bureau of Indian Standards. (6 ppm for Ca+2 as CaCO3. 4 ppm CO3-2 /HCO3- ).  

Calcium ion levels in Gematex boiler feed water sample is the highest among the boiler water samples of the four industries.

The situation of the results of the tested boiler feed water samples in the four companies highlighted the importance of more proper and perfect treatment and conditioning of the boiler feed water. The scales, corrosion, damage of boiler parts and low efficiency of the boiler may all be attributed to the presence of foreign elements like calcium ions found in the water.

Although the sulfate ion levels detected for Gematex company is the highest, these ions and the chloride ions are non-scaling. Their role in scaling and corrosion is insignificant as both ions are less-adherent slurry during boiling, and can be removed while the boiler blows down. 

 

 

 
CONCLUSION

 

All water samples of the boiler feed water for the four companies constitute various anions and cations with varying degrees.

Gematex company shows higher values of total hardness, calcium ions, carbonates and bicarbonates ions in their water sample.

K.S.C. and K.R.C. companies show lower levels of the mentioned ions because they are treating and conditioning their boiler feed water. High levels of total hardness, in the boiler water may cause problems concerning boiler performance.

It appears from the discussions that the water treatment process which is responsible for the removal of foreign elements from the boiler feed water is of absolute necessity if the boilers are to run without problems. pH specified standard values should also be maintained through dealkalization to avoid corrosion.

The four companies need proper treatments to bring the levels of concentrations of anions and cations of their boilers feed water within the recommended guidelines specified by ASME Guidelines or other standards.

A reliable water treatment unit is highly recommended for every mill adopting boilers for steam generation.

 A reverse osmosis system is to be added to the line of treatment as it removes physically all anions and cations from the boiler feed water. This is particularly recommended in wet textile processing while carrying certain dyeing and printing techniques.

Micro processing indicators that can digitally display chemical measurements of some properties of the treated water in – line with the treatment process is also recommended. This will show instantly the levels of foreign constituents in the boiler feed water.

Application of a genuine, stringent, legal, testing, training and certification systems to be imposed by the ministry of industry and to inspect periodically the conditions of the boilers of the various companies and factories in the country.

All the companies tested need to some extent proper revisions concerning their water treatment units. They must bring the chemical constituents of their boiler feed water to the levels specified by their boiler manufacturers. 

A further study is recommended to cover the effect of boiler feed water on the performance, efficiency, consumption of furnace fuel of industrial boiler. Also to compare that with production, expenses of repairing and of chemicals in washing.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Sendalbach,M.(1988). Boiler-water Treatment: Why, What and How. Chemical Engineering, 95(11),127.

V. Mallikarjuna, N. Jashuva, B.R.B. Reddy, (2014). Improving boiler efficiency by using air preheater,Int. J. Adv. Res. Eng. Appl. Sci., 3 (2014), pp. 11–24

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The Babcock and Wilcox Co, (2007). Steam its Generation and use (Thirty – Fifth Editions), Bartlett Orr Press, New York.

Babikir, (2016), Constituents of Feed Water and its Effect on Boilers Performance, University of Gezira.

http://www.gc3.com/Default.aspx ,(2016). An Introduction to Steam Boilers and Steam Raising.

http://nem.org.uk/steam.htm#top ASME Guidelines for Water Quality in Modern Industrial Water Tube Boilers.

Kartic K, Basak, Chattopadhyay, ( 2014). Eco-friendly Coloration and Functionalization of Textile using Plant extract- Springer.