GB2111179A

GB2111179A - Vermiculite as a deposit modifier in boilers

Info

Publication number: GB2111179A
Application number: GB08213589A
Authority: GB
Inventors: Gary Gene Engstrom; Douglas Ivor Bain
Original assignee: Dearborn Chemical Co
Current assignee: Dearborn Chemical Co
Priority date: 1981-12-10
Filing date: 1982-05-11
Publication date: 1983-06-29
Also published as: JPH044496B2; FR2518241B2; IT8224688A1; FR2518241A2; IE821122L; SE8206929D0; GB2111179B; NL8201903A; IE52749B1; BR8202671A; PT74870A; BE893135R; DE3245168C2; PT74870B; SE450580B; IT8224688A0; DE3245168A1; IT1155423B; SE8206929L; JPS58117912A

Abstract

Vermiculite is injected into a carbonaceous fuel-fired furnace, at 3000-1200 DEG F, to facilitate removal of fly ash deposits by steam or air blowers.

Description

SPECIFICATION Vermiculite as a deposit modifier in boilers The present invention relates to the use of vermiculite in furnaces.

The present invention provides a method of rendering fly ash deposits in a furnace more easy to remove by steam or air, which comprises introducing vermiculite into the furnace at a temperature of 3000 to 12000 F. In Application No.81 20104, to which reference should be made, there is described and claimed a method of rendering fly ash deposits in a solid carbonaceous fuel-fired furnace more easy to remove by steam or air, characterised by introducing vermiculite into the furnace at a temperature of 3000 to 12000 F. The present invention is applicable to furnaces which are fuelled other than by coal; also it has been found that it is not necessary to use uncalcined vermiculite.

Use of the present invention facilitates removal of deposits that form on the walls and heatexchange surfaces in an industrial furnace or utility boiler burning a solid carbonaceous fuel such as coal. This is accomplished by injecting vermiculite into the flue gas stream where the stream has a temperature of about 30000F to 1 2000F about 1 6750C to 645 OC), especially about 26000F (about 1 4300C) at a rate of 0.05 to 100 pounds of vermiculite (preferably 0.5 to 101bus) per short ton (2000 pounds) of coal burned, i.e. 0.0025 to 5%, preferably 0.025 to 0.5%, by weight.The vermiculite increases the friability of the deposits, making them easier to remove by conventional soot blowers, typically probes located within the boiler blowing in air or steam at, say, about 200 psig; 14 kg/cm2 gauge.

The mineral matter (ash) in coal, for instance, leads to deposits in the heat absorbing regions of the boiler, particularly the superheater and convection passes. These sintered fly ash deposits can be too strong for removal by conventional cleaning equipment. We have discovered that the injection of vermiculte will reduce the strength of deposits in order to maintain clean heat exchange surfaces and prevent the eventual blockage of these passages. In the past, the chemical and physical properties of materials such as magnesium oxide and alumina have been employed to interefere with sintered deposits.

Vermiculite is superior to these additives.

Vermiculite, a hydrated magnesiumaluminium-iron silicate, usually consists of 14 closely related micaceous minerals. When unexfoliated vermiculte is applied in such a manner as to be incorporated in the ash deposit and subjected to temperatures in the range encountered in superheater and convection regions, a dramatic reduction in the strength of the bonded deposit is evident. The unique properties which account for this activity includes thermally induced exfoliation (expansion) and the presence of a naturally occurring platelet structure (silica sheets) which acts as a cleave plane. Deposits can be removed with greater ease as a result of this treatment. Accordingly the use of uncalcined or unexfoliated vermiculite is preferred.

The vermiculite used should be relatively finely divided, suitably mostly 3 to 325 mesh (Tyler screen) (6.68 to 0.044 mm), and preferably mostly 28 to 200 mesh (0.595 to 0.075 mm).

A large number of solid carbonaceous fuels are available for use with vermiculite in the process of this invention. Such fuels include coal, lignite, peat, sunflower seed hulls, wood, wood waste, paper, paper byproducts, garbage, refuse derived fuels, sewage sludge, bagasse and plant byproducts. They can be used alone or in conjunction with each other and/or with gas or oil.

The following Example shows the effect of vermiculite on a furnace fired with sunflower seed hulls.

Example The boiler had a 40,000 pounds (18145 kg) steam/hour design capacity. It was stroker fired and burned approximately 80 tons per dayh of sunflower seed hulls. It was equipped with sootblowers.

Unexpanded vermiculite was blown into the furnace at 22000F (11 050C) at a rate of 8-10 Ibs/ton (0.04 to 0.05%) of hulls. The additive caused the deposits to be friable and readily removed by the sootblowers, resulting in clean tube and boiler surfaces which required no additional maintenance.

In contrast, in a comparable run but omitting the vermiculite, the deposits were hard, sintered, and bonded, making them impossible to remove with normal sootblowing. Deposits accumulated throughout the boiler, particularly at the inlet to the convective pass. The deposit build-up occurred in a matter of hours resulting in bridging between the tubes. These deposits had to be removed manually.

The terms "uncalcined", "unexpanded", and "unexfoliated" are all intended to mean the same thing, with reference to vermiculite. Unexpanded vermiculite was used in the Example. However, expanded vermiculite may also be used.

Claims

1. A method of rendering fly ash deposits in a solid carbonaceous fuel-fired furnace more easy to remove by steam or air, which comprises introducing vermiculite into the furnace at a temperature of 3000 to 12000 F.

2. A method according to claim 1 in which the vermiculite is injected into the furnace at the rate JO.5 to 10 Ibs/short ton of coal in said furnace.

3. A method according to claim 1 or 2 in which the vermiculite is 80 to 1 50 mesh (US Tyler sieve).

4. A method according to claim 1,2 or 3 in which the temperature of injection is about 26000 F.

5. A method according to any one of the preceding claims in which the fuel is coal, lignite, peat, sunflower seed hulls, wood, wood waste,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Vermiculite as a deposit modifier in boilers The present invention relates to the use of vermiculite in furnaces. The present invention provides a method of rendering fly ash deposits in a furnace more easy to remove by steam or air, which comprises introducing vermiculite into the furnace at a temperature of 3000 to 12000 F. In Application No.81 20104, to which reference should be made, there is described and claimed a method of rendering fly ash deposits in a solid carbonaceous fuel-fired furnace more easy to remove by steam or air, characterised by introducing vermiculite into the furnace at a temperature of 3000 to 12000 F. The present invention is applicable to furnaces which are fuelled other than by coal; also it has been found that it is not necessary to use uncalcined vermiculite. Use of the present invention facilitates removal of deposits that form on the walls and heatexchange surfaces in an industrial furnace or utility boiler burning a solid carbonaceous fuel such as coal. This is accomplished by injecting vermiculite into the flue gas stream where the stream has a temperature of about 30000F to 1 2000F about 1 6750C to 645 OC), especially about 26000F (about 1 4300C) at a rate of 0.05 to 100 pounds of vermiculite (preferably 0.5 to 101bus) per short ton (2000 pounds) of coal burned, i.e. 0.0025 to 5%, preferably 0.025 to 0.5%, by weight.The vermiculite increases the friability of the deposits, making them easier to remove by conventional soot blowers, typically probes located within the boiler blowing in air or steam at, say, about 200 psig; 14 kg/cm2 gauge. The mineral matter (ash) in coal, for instance, leads to deposits in the heat absorbing regions of the boiler, particularly the superheater and convection passes. These sintered fly ash deposits can be too strong for removal by conventional cleaning equipment. We have discovered that the injection of vermiculte will reduce the strength of deposits in order to maintain clean heat exchange surfaces and prevent the eventual blockage of these passages. In the past, the chemical and physical properties of materials such as magnesium oxide and alumina have been employed to interefere with sintered deposits. Vermiculite is superior to these additives. Vermiculite, a hydrated magnesiumaluminium-iron silicate, usually consists of 14 closely related micaceous minerals. When unexfoliated vermiculte is applied in such a manner as to be incorporated in the ash deposit and subjected to temperatures in the range encountered in superheater and convection regions, a dramatic reduction in the strength of the bonded deposit is evident. The unique properties which account for this activity includes thermally induced exfoliation (expansion) and the presence of a naturally occurring platelet structure (silica sheets) which acts as a cleave plane. Deposits can be removed with greater ease as a result of this treatment. Accordingly the use of uncalcined or unexfoliated vermiculite is preferred. The vermiculite used should be relatively finely divided, suitably mostly 3 to 325 mesh (Tyler screen) (6.68 to 0.044 mm), and preferably mostly 28 to 200 mesh (0.595 to 0.075 mm). A large number of solid carbonaceous fuels are available for use with vermiculite in the process of this invention. Such fuels include coal, lignite, peat, sunflower seed hulls, wood, wood waste, paper, paper byproducts, garbage, refuse derived fuels, sewage sludge, bagasse and plant byproducts. They can be used alone or in conjunction with each other and/or with gas or oil. The following Example shows the effect of vermiculite on a furnace fired with sunflower seed hulls. Example The boiler had a 40,000 pounds (18145 kg) steam/hour design capacity. It was stroker fired and burned approximately 80 tons per dayh of sunflower seed hulls. It was equipped with sootblowers. Unexpanded vermiculite was blown into the furnace at 22000F (11 050C) at a rate of 8-10 Ibs/ton (0.04 to 0.05%) of hulls. The additive caused the deposits to be friable and readily removed by the sootblowers, resulting in clean tube and boiler surfaces which required no additional maintenance. In contrast, in a comparable run but omitting the vermiculite, the deposits were hard, sintered, and bonded, making them impossible to remove with normal sootblowing. Deposits accumulated throughout the boiler, particularly at the inlet to the convective pass. The deposit build-up occurred in a matter of hours resulting in bridging between the tubes. These deposits had to be removed manually. The terms "uncalcined", "unexpanded", and "unexfoliated" are all intended to mean the same thing, with reference to vermiculite. Unexpanded vermiculite was used in the Example. However, expanded vermiculite may also be used. Claims

5. A method according to any one of the preceding claims in which the fuel is coal, lignite, peat, sunflower seed hulls, wood, wood waste, paper, paper byproducts, garbage, refuse derived fuels, sewage sludge, bagasse or plant byproducts.

6. A method according to claim 5 in which the fuel is sunflower seed hulls.

7. A method according to any one of the preceding claims in which the vermicupite is uncalcined.

8. A method according to claim 1 substantially as described in the Example.