FR2518241A2 - PROCESS FOR MAKING THE FLY ASH IN A BOILER FRIENDY BY MEANS OF VERMICULITE - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR MAKING FLY ASH DEPOSITS MORE FRIENDLY IN A SOLID CARBON FUEL OVEN, SO AS TO FACILITATE THEIR REMOVAL BY AN AIR OR STEAM PROBE. ACCORDING TO THE INVENTION, UNCALCINATED VERMICULITE IS INJECTED INTO THE OVEN AT A TEMPERATURE OF 1650-650C. THE INVENTION APPLIES IN PARTICULAR TO THE REMOVAL OF DEPOSITS FORMING ON THE WALLS AND HEAT EXCHANGE SURFACES IN INDUSTRIAL OVENS OR BOILERS.

Description

The use of the present invention facilitates the removal of deposits

  which are formed on walls and heat exchange surfaces in an industrial furnace or in a carbon fuel boiler This is accomplished by injecting an effective amount of uncalcined vermiculite into the stream of flue gas where the current

  at a temperature of the order of 1650 to 6500 C, advantageously

  at a rate of 0.025 to 50 kilograms of vermiculite

  (preferably 0.25-5 kg) per ton of fuel burned.

  Vermiculite increases the friability of deposits, making them easier to remove by traditional soot blowers (such as probes placed in the boiler,

  blowing air or steam at about 13.8 bar).

  The mineral material (ash) in solid carbonaceous fuels, such as coal, leads to deposits in the heat absorption regions of the boiler,

  in particular the superheater and the convection passages.

  These agglomerated fly ash deposits may be stronger than the potential of traditional cleaning equipment. It has been discovered that vermiculite injection can reduce the strength of the deposits to keep the heat exchange surfaces clean. and to prevent

  the possible blockage of these passages.

  Vermiculite, a mineral naturally occurring

  expands up to 15-20 times its original volume when exposed to temperatures above about 6500 C. This greatly reduces the strength of agglomerated (bonded) deposits where vermiculite is present In the past, the properties Chemical and physical materials such as magnesium oxide, alumina and others, were used, to interfere with the deposits

  Vermiculite is superior to these additives.

  Vermiculite, magnesium aluminum silicate

  hydrated iron, consists of 14 closely related micaceous minerals When non-exfoliated vermiculite is applied to be incorporated into the ash deposit and is subjected to temperatures in the ranges encountered in the superheater-and convection regions a dramatic reduction in the strength of the bonded deposit is evident The unique properties allowing this activity include thermally induced exfoliation (expansion) and the presence of a natural platelet structure (silica sheets) which acts as a cleavage plane. deposits can be removed more easily

as a result of this treatment.

  As far as is known, non-calcined vermiculite has never been injected at the hot end of an oven for any purpose. In an earlier reference, calcined (expanded) vermiculite was injected into the end of the furnace. cold oven (82-1820 C) to absorb

  sulfuric acid deposited on the metal surfaces.

  B L Libutti, C Centennial Meeting, New York, N Y.

  April 4-9, 1976, "Symposium on Heavy Fuel Oil Additives".

EXAMPLE I

  The boiler had a rated capacity of 347 megawatts. It was cyclone and burned bituminous coal c eastern or eastern It was equipped with soot blowers Un-expanded vermiculite was blown into the furnace at 14270 C at 0 , 3-0.7 kg / ton

  The additive made the deposits online

  friable to be easily removed by

soot blowers at 13.8 bar.

  On the contrary, in a comparable test but omitting vermiculite, the deposits were hard, agglomerated and stuck, making them difficult to detach and dislodge.

by means of steam probes.

  It is preferred that the vermiculite is relatively finely divided, i.e., it preferably corresponds to a mesh size of 3 to 325 for Tyler sieve, and more preferably 28 to 200, for Tyler sieve. The product in the present example above and to the tables corresponded mainly to

  a Tyler mesh screen having about 80-150 mesh.

  Solid addition device In the above example, air-cooled probes were used to inject vermiculite into the furnace. The probe was about 9.14 meters long and was constructed in a single tube. Steel Vermiculite is removed from a hopper by means of a screw feeder that doses the vermiculite into an air transport system that brings the vermiculite to the probe. The airflow cools the probe while the vermiculite is fed. at

Boiler.

  The agglomeration test developed by Babcock and

  Wilcox was used to determine the tendency to foul

  The formation of bonded deposits of various ashes and the effect of the additives can be referred to DH Barnhart's The Sintering Test, An Index to AshFolding Tendency and PC Williams, Transactions of the ASME, August 1956, page 1229. Briefly, the test consists of forming pelletized ash, heating at various elevated temperatures for 15 hours and measuring the force required to grind the resulting agglomerated samples. Table 1 summarizes the results obtained without additives, with various levels of vermiculite and with magnesium oxide, for a bituminous coal ash from the east Magnesium oxide has been found to have the greatest effect in reducing the agglomeration force in the work done by Babcock and Wilcox, and Table 1-a repeats the averages given in Table 1 and gives further data for 871 WC and gives the number of pellets tested (in parentheses). es

  Tables 1 and 1-a are based on the weight of the ashes.

  The percentages in Table 2 are based on the data

from Table 1-a.

TABLE 1

  Agglomeration force of the pellets, 105 Pa

982 C

10930 C

  Virgin 746.28 1050 926 1769 (Without treatment) 898 1002 536 1548

774 1057 1720 1334

  Virgo on average 921 1306 Vermiculite, 0.5% 454 678 884 974

690,712,843,988

529,598

  Average 0.5% 612 858 Vermiculite, 1.0% 448 497 424 423.5

359,366,421,471

453 691 404 479

  J, Mean 1.0% 469 437 Vermiculite, 1.5% 343 312 337 310

345,273,342,269

383,261,290,295

  Average 1.5% 319 307 Magnesium oxide, 1.5% 574 560 891 933

464,447,712,726

587,357,1002

Average 1.5% Mg O 498 853

Table 1-a

  Average Agglomeration Strength, 105 Pa (Number of pellets tested) Identity 871 C 982 C 10930 C Virgin 191 (9) 919 (6) 1302 (6) Vermiculite, 0.5% 138 (9) 611 (5) 855 ( 5) Vermiculite, 1.0% 61 (9) 468 (6) 436 (6) Vermiculite, 1.5% 57.5 (9) 318 (6) 306 (6) Mg O, 1.5% 100 (8) ) 497 (6) 851 (5)

Table 2

  Percentage reduction in agglomeration force Identity 871 C 982 C 1093 C Virgin Vermiculite, 0.5% 27.7 33.5 34.3 Vermiculite, 1.0% 68, 3 49.1 66.5 Vermiculite, 1 , 5% 70.0 65.3 76.5 Mg O, 1.5% 47.5 45.9 34.7 Table 3 summarizes the data obtained with various additives on a second sample of bituminous coal ash from the Percentages are based on ash weight Numbers in parentheses indicate the number of pellets tested Table 4 restores the data in Table 3, in terms of percentage reduction of agglomeration force compared to virgin These results demonstrate the effectiveness of

  vermiculite to reduce the agglomeration force.

2518 41.

251824 he

Table 3

  Average Agglomeration Strength, 105 Pa (number of pellets tested) Identity Virgin Vermiculite, 1.5% Titanium Dioxide, 1.5% Silicon Dioxide, 1.5% Talc, Oxide Oxide Oxide 1.5% Aluminum , 1.5% magnesium, 1.5% calcium, 1.5%

871 C

174 (6)

51 (6)

127 (6)

(6) (6) (5)

41 (5)

69 (5)

982 C

1124 (6)

307.5 (6)

751.5 (4)

(5) (6) (6)

696 (6)

765 (6)

Table 4

  Percentage reduction in agglomeration force Identity Virgin Vermiculite, 1.5% Titanium dioxide, 1.5% Silicon dioxide, 1.5% Talc, 1.5% Aluminum oxide, 1.5% Oxide magnesium, 1.5% Calcium oxide, 1.5%

871 C

, 6 27.3, 2 63.6, 76.3, 5

982 C

  72.6 33.1 3.7 22.7 Increase 38.0 31, 9

* 1093 C

  81.4 17.2 Increase Increase Increase 33.1 33.1 A large number of carbonaceous solid fuels are available for use with vermiculite in the process according to the invention. Such fuels include coal, lignite, peat, sunflower seed shells, wood, wood waste, paper, paper by-products, garbage,

1093 C

2523 (3)

469 (3)

2089 (3)

  (3) (3) (3) (3) (3) fuels derived from residues, sludge,

  bagasse, treatment by-products and the like.

  They can be used alone or with each other or

with gas or oil.

  The following example shows the effect of vermiculi on a kiln operating with sunflower seed shells.

EXAMPLE 2

  The boiler had a nominal capacity of 18,200 kilograms of steam per hour. It burned about 50,000 tons per day of sunflower seed husks. It was equipped with soot blowers. The unexpanded vermiculite was blown into the water.

  the oven to 1204 WC at a rate of 4-5 kg / ton of hulls.

  The additive made the deposits brittle and easy to remove by the sootblowers, resulting in clean E-surfaces of the tubes and the boiler, without requiring

additional maintenance.

  On the contrary, in a comparable test but omitting vermiculite, the deposits were hard, agglomerated and stuck, making them impossible to remove by means of a normal soot blowing. The deposits accumulated throughout the boiler, particularly in the entrance to the convection passage Accumulation of deposits occurred in a few hours, resulting in connections between the tubes These deposits had to be removed

by hand.

  In this description, the terms

  calcined, unexpanded and not exfoliated are all intended to

  mean the same thing, referring to vermiculite.

  In the examples, unexpanded vermiculite was used in its prepared form. However, calcined vermiculite (i.e.

dilated or exfoliated).

Claims (9)

R E V E N D I C A T IO N S   A method for rendering fly ash deposits more friable in a solid carbonaceous furnace, thereby facilitating their removal by a steam or air probe, characterized by injecting an effective amount of vermiculite into the oven at 1650-650C.   2. Method according to claim 1, characterized in that the aforementioned vermiculite is injected with   about 0.25-5 kg / ton of fuel.   3. Method according to claim 1, characterized in that the vermiculite corresponds to a mesh of 80 to on a Tyler sieve.   4. Process according to any one of   preceding claims, characterized in that the   injection temperature is of the order of 1427 C.   5. Method according to claim 1, characterized in that the fuel is selected from the group consisting of coal, lignite, peat, sunflower seed hulls, wood, wood waste, paper, paper by-products, garbage, fuels. derived from residues, sludge   spreading, bagasse and processing by-products.   6. Method according to claim 5, characterized   in that the fuel is coal.   7 Process according to claim 5, characterized in that the fuel is formed of sunflower seed shells. 8. Process according to any one of   preceding claims, characterized in that the vermiculite is not dilated.   9. Process according to any one of   Claims 1 to 7, characterized in that the vermiculite is dilated.