Steam Boiler: Soot Blowing System

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Design Soot Blowing System

The design soot blowing system should furnish well experienced and approved steam jet type sootblowers for the superheater, generating bank, economizer and air heater. The design soot blowing system should arrange the sufficient number of sootblowers for the above mentioned equipment.

If additional soot blowing equipment is necessary to maintain the proper surface conditions of superheater, generating bank, economizer, or air heater, additional equipment with all piping and wiring should be furnished without any addition to the contract price during the guaranteed period.

A complete soot blowing system consisting of all controls, actuators, piping, valves, control panels, including all necessary starters, switches, relays, protection devices, etc., should be provided. Steam from high pressure auxiliary steam header should be used as the cleaning medium. An air operated isolating valve controlled from the remote control panel should be provided to allow isolation of the soot blowing steam.

Complete remote control system for each sootblower, including all switches, relays, signal lamps, sequences, etc., should be provided and installed in the central control room to supervise operation of blowers.

The system should be able to allow local manual operation of each sootblower in case of test or failure of remote control system. The remote control panel should be of the mimic type suitable for flush mounting. The panel should be complete and fully wired and tubed with clearly identified terminal blocks and strips.

The panel should be mounted on the auxiliary control panel in the central control room. All motor starters for the boiler sootblowers should be furnished. Motor starters should be of magnetic type mounted on each sootblower with thermal trip relays and start-stop push buttons for local operation.

Retractable sootblowers should be provided with a hand crank or drive nut for withdrawing the lance tube in case of power failure. Sootblowers should be installed in such a manner as to permit boiler expansion without binding or unbalanced loading. A complete system of sealing air piping should be furnished to seal the wall sleeves if necessary.

A complete system of aspirating air piping to permit removal of blower of should be furnished if necessary. Sealing air and aspirating air piping should have flexible hoses to permit boiler expansion without binding.

Any drain attack due to soot blowing on superheater, generating bank, economizer and air heater element should be absolutely prevented. Special consideration should be given to the method of efficient draining and heat insulation. Any other cleaning system on heating surfaces of flue gas side should be given a special consideration and should be approved by the engineer.

Boiler Sootblower

Boiler sootblower is one of important equipment to maximize steam boiler efficiency. Efficiency of boiler is influenced mostly by heat transfer process. One among the most necessary operations to increase heat transfer process is clean metal surfaces for absorb heat. The cleaning metal surfaces is performed to ensures appropriate heat transfer process and in addition avoids parts of steam boiler from growing to be plugged and blocked. Plugged parts could limit gas circulation and lead to load restrictions.

Boiler sootblower is specially needed on coal fired boiler and oil fired boiler. If oil fuel consist of low content of ash and generate small residue, the cleaning method of furnace wall can be performed by water washing for the duration of twelve-monthly shutdown. This is why; boiler sootblower which is installed on furnace wall is not needed on the oil fired boiler.

In the reheater and superheater parts of oil fired boiler, there's ash accumulation on metal surfaces. Excessive-oil vanadium subject matter that contains chemicals to resist high-temperature corrosion, tend to be specifically vulnerable to the following. However while solid powder chemicals are utilized, the deposits of ash boost seriously in the high temperature of gas locations. The good thing is, the deposits fall and easily cleaned with boiler sootblower.

Coal fired boiler need many sootblower which is installed permanently. Reasons like high content of ash and ash-fusion temperatures determine simply what exactly sootblowing area is needed. Boiler sootblower usually utilizes compressed air or superheated steam as medium to eliminate deposits, utilizing rotary or retractable types. The efficient blowing regularity varies according to slag accumulation; however a usual could be four until eight hours. The steam boiler parts such as reheater and superheater is suitable to use long retractable type of sootblower to clean radiant heat surfaces.

Classification of Soot Blower

Fig.1: Long Retractable Soot Blower

Soot blowers that are installed in steam boiler commonly can be classified as:

1. Long Retractable Soot Blower

This type of soot blower is located in area superheater and reheater. There is not temperature limitation in its use. Has a pair (2) of nozzle in lance tube located on both side in exact opposition (angle 0^o and 180^o) with diameter approximately 22 or 25 mm. The steam flow through soot blower is approximately 4 to 20 tph. Need more space to place long retractable soot blower on the sides of steam boiler.

Fig. 2: Wall Soot Blower

2. Wall / Short Retractable Soot Blower

This type of soot blower is located in area furnace. There is not temperature limitation in its use. Has 1 or 2 nozzle in lance tube with diameter approximately 25 mm. The steam flow through soot blower is approximately 3.5 tph. Mostly used in high temperature furnace of Pulverized Fuel Boiler. One soot blower is required to blow furnace area in every 10 m².

3. Rotary Soot Blower

Fig 3: Rotary Soot Blower

This type of soot blower is located in area boiler bank, economizer, and air heater. Its use is limited to temperature 1100^o C. Have many nozzles in lance tube with diameter approximately 8 mm. The steam flow through soot blower is approximately 3.5 tph. Maximum lance length is limited until 7 m, if the steam boiler larger than 7 m, so soot blower will be installed in both sides and can be operated by motor or manual.

4. Rake Soot Blower

Fig. 4: Rake Soot Blower

This type of soot blower is located in area fin tube economizer and vertical tubular air heater. Its use is limited to temperature 530^o C. Have many sets of nozzle. The steam flow through soot blower is approximately 3.5 – 4.5 tph. Dimension of rake soot blower is limited to 5 m length and 3 m width.

Soot Blower of Steam Boiler

Fig. 1: Soot Blower of Steam Boiler

Soot blowers is mechanical device automatically controlled to deliver intermittent jet of compressed steam or air to clean ash, soot, slag from heat absorbing surfaces by blowing on the surface. Soot blower is used eliminate slag, so maintain efficient flue gas temperatures and generally promote more desirable operating conditions. Determination of location soot blower is important to design new steam boiler.

Many installtions of steam boiler are now designed to use more boilers and they depend on the type of steam boiler size, firing, fuel type, ash in fuel, slag potential, previous experience, etc. Soot blowers remove soot and ash deposits from the fire sides of heating surfaces so that they remain optimally clean and heat transfer is maintained at the original design levels. Slagged area can be cleaned periodically and one at a time.

Steam boiler tubes and heating surfaces get dirty because of accumulation of slag. With excessive slag, the waterwall absorb less heat because slag is a good insulator and reduce the effectiveness of heating surface, so decrease load and increase steam temperature beyond control limit. Every effort must be made to avoid slagging passes in the boiler. The increase in steam boiler maintenance resulting from slgging at high furnace exit temperature is well known.

For water tube boiler, soot blowers are commonly used and permanently installed but not very effective for firetube boiler. Soot blower has element that are located in the direct path of the products of combustion. Steam is blown from the nozzle in the elements at high velocity between the rows of tubes.