Stewing and Blow-out of Steam Boilers with HELAMIN®

• Introduction
• Advantages, mode of operation, disadvantages of the classic methods
• Operating instructions for stewing with HELAMIN®
• Blow-out of the piping system, control mirror
• Product descriptions
• References

Introduction

New water tube boilers are often very strongly fouled with rolling skin, iron, oil and grease. This can lead to considerable depositions and corrosion at start-up of the boiler, particularly at the downstream turbines.

In practice, all components in contact with water are therefore stewed under addition of alkaline chemicals before the boiler is commissioned.

In the past conventional, classic chemicals, like trisodiumphosphate or bicarbonate lye (caustic soda), were used alone, or in various combinations.

During the last few years considerable damage has been caused by improper use of conventional chemicals, in particular caustic soda.

Due to more and more strict limits for disposing boiler water into the sewage system, environmentally friendlier, easier to handle chemicals were sought.

For over 15 years an alternative has been available with our special HELAMIN® grade for stewing boiler systems; and in the past few years it has been used by many boiler manufacturers with great success.

The patented action, the simple handling, as well as the toxicological and ecological safety of our HELAMIN® products have led to these decisions.

In addition, there is no danger of stress corrosions cracking with HELAMIN® as is with, e.g. caustic soda.

The following recommendations are the result of our long-standing experience, incorporating the recommendations by boiler manufacturers, VGB and turbine manufacturers.

Advantages

• Easy handling and working with HELAMIN®
• Reduced safety requirements (only safety goggles and protective gloves) when filling the system
• No storage regulation (WGK 1)
• Disposal conditions of the local authorities can be met without problem (pH - value, CSB, TOC etc.)
• More thorough cleaning of the plant of grease, oil, rolling skin and iron oxides by the special combination of "film forming" polyamines and polyacrylates
• Formation of a good magnetite protective film already during stewing
• Steam purity is achieved with considerably fewer blow-out cycles leading to time and, in particular, cost savings
• Shortening of rinse and idle periods also results in a reduction of operating costs

Effect of HELAMIN® on the Surface of C-Steel

Experiment: The surface of an iron sheet was polished and subjected to various water conditions in a laboratory autoclave:

1. demineralised, deaerated water, alkaline

2. as above, but with 20 ppm HELAMIN®

After every step the water was changed.

magnetite Crystals Experiment 1 classic	magnetite Crystals Experiment 2 with HELAMIN®

Disadvantages of the classic methods

Trisodiumphosphate:

• difficult to dissolve in the water
• can result in phosphate deposits in the tubes
• no dispersing capabilities
• not volatile
• problematic disposal into water or sewage system
• tendency of foaming when over-dosed
• danger of hide-out effect
• longer blow-out times

Bicarbonate lye or caustic soda:

• no dispersing capabilities
• not volatile
• problematic handling
• caustic burns
• danger of stress corrosions cracking
• rather long blow-out period

Demineralised water:

• no dispersing capabilities
• no cleaning capability
• rather long stewing and Blow-out period
• not volatile

Operating instructions for drying, stewing and blow-out of steam-boilers with HELAMIN®

Introduction:

The following stewing instructions are based on the experience of the manufacturer in collaboration with leading experts of the boiler industry. Deviations from the instructions, based on specialists considerations, are possible; this should, however, be done in consultation with a HELAMIN® specialist.

1. Drying of the brickwork

Drying of the brick work is required to cure and sinter the masonry material and to ensure that there is no more liquid left in the brick work. At same time a permanent bonding of the tube walls with the brick work is achieved. The temperature increases and the duration of temperature hold are given by the instructions of the masonry company (see 8.1)..Combined with the drying process, stewing of the boiler can already be started. (see 6.6)

2. Stewing of the boiler system

Stewing the boiler system cleans it of grease, shavings, loose tinder and dirt residues that remain from the manufacturing and installation of the boiler.. .

3. Conditions for stewing

Certain conditions must be fulfilled before stewing can be started:

• the combustion plant must be ready for firing.
• supply of feed water must be guaranteed for the whole duration of the stewing process.
• the feed water control valve must be controllable by hand.
• water level control and water level indicator must be operational.
• the start-up valve must be operational.
• all safety features of the boiler must operational and activated.
• all openings at the boiler must be closed.

4. Rinsing and filling of boiler

4.1 Feed water requirements.

For two stewing cycles and the blow-out(s), a volume of approximately 10 x the volume of the boiler is required.

Example: Boiler volume 17 m³

Approximately 5 m³ of feed water are required for each blow-out. Not included in above is the volume required for starting up and for shutting down.

No indication can be given for the number of blow-outs required .

4.2 Rinsing and filling.

• drum vent: open.
• start-up valve: open.
• all drains: open.
• manhole of the drum: open..

For these operations the feed water flow rate should not exceed 20% of the boiler capacity

Watch the drains; as soon as water flows, the respective drain is to be closed after approximately one minute rinse time..

Once all drains are closed, filling can be started

During the filling process the required chemicals are added (see point 5)

Observe the filling through the manhole of the drum. If the boiler, or the drum respectively, is filled above the exit of the downer pipes the process is interrupted. The chemicals prepared according to point 5 are added, the manhole carefully closed and the boiler filled to normal water-level.

If the chemicals are added via the feed water line, the drum can be closed once feed water enters the drum. The water level is to be observed through the water level indicator.

5. Stewing chemicals

For stewing HELAMIN® BRW 150 H is used..Helamin is a blend with a pH of 11.5.

With HELAMIN® two stewing cycles are sufficient.

The following volumes of Helamin are required for stewing:

6. Stewing operation.

6.1 1st 24 hour stewing operation

Stewing can be carried out at atmospheric pressure or with closed boiler, since at higher temperature the cleaning process is accelerated. The pressure should be about ? of the operating pressure.

Pressure is controlled with the start-up valve. As soon as steam escapes at the respective vents they are to be closed. Stewing is carried out for about 24 hours

6.2 Emptying of boiler.

After stopping the supply of heat, feed water has to be provided until the water level of the drum does not drop anymore.

The start-up valve is opened completely. When the system is at atmospheric pressure the boiler is emptied, rinsed and re-filled.

6.3 2nd 24 hour stewing operation

The second stewing operation is carried out as under points 6.1 & 6.2 except that the volume of HELAMIN® is halved.

6.4 Rinsing of boiler

After final stewing the boiler is thoroughly rinsed (2 x) and re-filled.

6.5    Evaluation of the stewing process.

HELAMIN® excess is an indication of the cleaning effect. During the 1st stewing process the water should have an excess of approx. 100 mg/l.

This excess is to be determined every 6 hours.

During the 2nd stewing process the HELAMIN® excess should preferably remain constant.

If the HELAMIN® excess does not drop anymore the stewing process is completed..

6.6    Stewing "under operation" (e.g. when drying brick work)

When stewing "under operation" a HELAMIN® addition of 1liter per m³ boiler volume should be added as mentioned under point 5. HELAMIN® excess of 100 mg/l should be maintained by dosing of approx. 1.0 liter HELAMIN® pro m³ water added.

When no drop in HELAMIN® excess can be noticed anymore the stewing process is completed and one proceeds as described under points 6.2, 6.4 & 6.5.

Note: The flue gas temperatures are to be measured and recorded during all stewing cycles!

7. Blow-out of the boiler system.

Blow-out is required to clean all heating surfaces (super heater) downstream of the boiler that could not be stewed, as well as the steam piping leading to the plant.

Blow-out is particularly required with turbine operation to avoid damage to the turbine. The steam purity is determined by means of an aluminum or copper mirror that is installed in the blow-out line. The mirror is examined by a representative of the turbine manufacturer.

The mirrors required are numbered. The number of blow-out and the condition of the respective mirrors is recorded.

Blow-out is completed if the mirror shows no or only insignificant indentations or if the person responsible for the blow-out declares it completed.

During the entire blow-out process the water level has to be controlled by hand.

7.1 Blow-out operation.

1. The boiler is brought up to the required temperature and combustion stopped.
2. All steam lines and the blow-out line are thoroughly drained and preheated.
3. The blow-out valve is opened, the start-up valve closed. Each single blow-out lasts for about 5-6 minutes.
4. As soon as the blow-out valve is opened, feed water supply is to be opened fully. The intense steam formation in the drum (due to the sudden pressure drop) results in the indication of a false water level (water consumption).
   When closing the blow-out valve the volume of feed water is to be reduced and adjusted.
   Before closing the blow-out valve the start-up valve is to be opened fully.
5. Reduce pressure and temperature.
6. When the boiler has cooled down a further blow-out can be prepared (if required).
7. Start at point 1 again.
8. To achieve high steam velocities, resistance has to be kept as low a possible.

What has to be taken into account when stewing:

• Use of the right product: HELAMIN® BRW 150 H for industrial boilers, HELAMIN® 2024 HUM in food processing plants
• HELAMIN® excess during the first stewing process should be approx. 100 mg/l.
• For the second stewing process approx. 30 -50 mg/l HELAMIN® excess is sufficient.
• If the boiler is stewed while drying the brick work, the HELAMIN® excess should be at least 100 mg/l.
• This is due to the low stewing temperature.
• The pH should adjust itself to approx. 10.
• To promote the formation of the protective magnetite film, stewing temperatures should be as high as possible.
• Additional water, containing oxygen, accelerates the formation of the protective magnetite film to a certain degree.
• It should be ensured that in the stewing process of a boiler all drains, e.g. drain manifolds or take off points for sampling are sufficiently rinsed and drained.

Methods of steam exhaust

Exhaust of steam into the atmosphere

With this method the steam is blown into the atmosphere, producing a high noise level. Silencers can reduce the intensity of noise. This method is used only there where the high noise level is un-acceptable.

Exhaust of steam into waters

The noise level is reduced considerably by releasing the steam under water. With this method the allowable heat load for the waters has to be considered as well as the possible impact by possible foreign substances.

Exhaust of steam into condenser

This method is chosen if the two previous ones cannot be used.

Advantage:

• Low noise level
• Minimal work for temporary blow-out arrangements
• Recovering of the condensate

Disadvantage:

• Danger of damage to valve seats and condenser tubes by foreign bodies
• Only lines that are part of the bypass can be blown-out
• Possible pollution of the water cycle

The particles blown out leave the line at high velocity. Suitable measures should be taken to avoid damage to persons or equipment by these particles.

Inspection of Piping

Inspection of steam purity

The result of a blow-out is evaluated using a device as described & shown below.

Device 1 consist of a holder (4) and a control plate (3) made of steel, copper or aluminum of approx. 40 mm of width and min. 1 mm of thickness.

Device 1

Device 2 consists of a steel mirror fastened to the top and the bottom of the pipe.

Device 2

The mirrors should be used on both sides and replaced after every blow-out.

Result of a Blow-out and Evaluation

The particles carried by the blow-out steam leave indentations on the surface of the mirror installed. The number, size and formation of the edge of the indentations determine the result of the blow-out. After every blow-out the number of indentations should drop and, at the end, remain constant. Blow-out is terminated if the operator and the manufacturers of the boiler and of the steam turbine confirm adherence to the recommendations on indentations given below.

VGB recommendation

no indentation > 1 mm
less than 4 indentations > 0.5 mm
less than 10 indentations > 0.2 mm

ABB Turbinen GmbH

no indentations > 0.8 mm in diameter
no more than one indentation of 0.4 mm on an area of 50 mm x 50 mm
no more than five indentations of 0.2 mm
indentations < 0.2 mm should not show a cluster pattern

Independent of the steam purity, a strainer is installed at the steam inlet to the turbine before commissioning and cleaned during service.

Product Data Sheet

EU, data sheet HELAMIN® BRW 150 H

Please click here to view product data sheet

Reference

Reference Extract for Stewing of Boiler

Reference Stewing GTA, Gendorf

Memorandum: AHDE Stewing

Dear Sirs,
On 21.01.02 the stewing of the HP boiler and of the LP system was as planned successfully completed.

Visual examination of the water samples taken water showed a considerable reduction of the undissolved substances and of discoloration at the end of the 2nd stewing cycle.

The drum inspection with it has AG represented devotedly to satisfactory cleaning effect and protective coating education, by H. Redinger and H. Heidrich.

Redinger Heidrich

Infraserv- Infraserv--

The result of the laboratory analyses of the samples will be submitted later.

Positions 34, partially and 232 - 234 of the commissioning programme are herewith completed.

We are ready to proceed with position 235 of the commissioning programme on 22/01/02.

With kind regards
pp Neitzke

Attachment: diagrams of data acquisition 17 - 20/01/02 SKG

LP – Drum 21.01.2002

HP – Drum 21.01.2002