CS253054B1 - Method of cement clinker firing with coal wastes utilization - Google Patents

Abstract

The solution relates to the firing of cement clinker. The purpose is to use less fuel and save noble fuel. This is accomplished by the fact that in one and / or more burners of the firing unit, e.g., a rotary kiln, a noble fuel with a calorific value above 23 IU / kg is burned simultaneously with the coal waste with a calorific value of less than 17 IU / kg. an ash content of more than 30%, the amount of which is due to the chemical composition of the ash from these wastes and the noble fuel, together with the chemical composition of the cementitious mix as a function of the required silicate modulus Mg = 1.8 to 3.0, the aluminate module Ma = 1, 5 to 4.0 and lime slp = 90 to 100 of the resulting Portland clinker, the theoretical combustion temperature of the resulting fuel blend being greater than 1700 ° C.

Description

The invention relates to a method for firing cement clinker using coal waste.

Cement clinker firing is currently carried out mainly in rotary kilns using rotary kilns using high-quality gaseous, liquid or solid fuels, ie mainly fuel oil, natural gas and hard coal with a calorific value above 23 MJ.kg \ Solid fuels with a calorific value below 23 MJ.kg are unsuitable for firing cement clinker due to the low combustion temperature.

Occasionally brown coal and lignite are also used for firing clinker, but only with calorific values and composition guaranteeing in the dried state combustion temperatures at the level of combustion temperature of black coal with the calorific value of 23 MJ.kg.

The disadvantage of the current situation is the lack of quality fuels and their increasing price. The possibility of partially replacing these fuels with lower calorific or lignite charcoal causes an increase in the specific heat consumption and hence an absolute fuel consumption, despite the fact that the proportion of this fuel is limited by the ash content and composition. From an economic point of view, the use of lower quality solid fuels means some extra costs for their transport, treatment and drying, as opposed to the use of the original one-component fuel.

The above drawbacks are overcome by the method of firing cement clinker, which consists in the fact that in one and / or more burners of a burning unit, eg a rotary kiln, noble fuel with a calorific value above 23 MJ.kg is simultaneously burned with coal waste less than 17 MJ.kg with an ash content of more than 30%, the quantity of which is determined by reference to the chemical composition of the ash from these wastes and the noble fuel, together with the chemical composition of the cementitious cement mix, 3.0, an aluminate module M = = 1.5 to 4.0 and lime saturation S _Lp = 9 až to 100 of the resulting Portland clinker, wherein the theoretical combustion temperature of the resulting fuel mixture must be greater than 1700 ° C.

In this way, noble fuels such as fuel oil or natural gas can be partially replaced by low-grade solid fuels, such as coal wastes. Even such a partial substitution of the production of noble fuels represents a significant reduction of production costs during the firing of cement clinker.

The invention will now be explained in more detail by way of examples.

The determination of the amount of low-grade fuel that can be burned without affecting the quality of the resulting product is based on the following relationships:

S silicate module M_ = S a + F aluminate module M _a = AF lime saturation S _Lp

C

2,85.S + 1,18.A + 0,65F where C is the CaO content in% by weight

S is the SiO2 content in wt.

A is the content of alumina AJ? Og in wt.

F is the iron oxide content ⁱⁿ F®2 ° 3% ^ ^mot · in which the contents of oxides are based on either the clinker or the raw material.

Theoretical combustion temperature ^Q n ^{+ Q} CO 2 ^{+ Q} H ² O ^{+ Q} VZ

T. _

B + D + E + G + H + J + X + Y where Q _n is the fuel calorific value (kJ.j of fuel)

Q _what is the chemically coupled heat of dissociated carbon dioxide fractions (kJ.j ^{1 of} fuel)

QfO ~. Q ^lu 2 2 2 CO where </ cQ 3 ^{e the} degree of dissociation of CO 2

- * Λ

3-1 ^In CO2 ° kj ^ein CC> 2 in flue gas (IU fuel) 3

Q is dissociation heat of CO ₉ to CO (kj.m)

CO '_] _ θ is the chemically coupled heat of dissociated proportions of H ^ O (kJ.j of fuel) ³ HO rf' O ' ^V HO' ^Q n 2 ₂ ^{2 H} 2 where the degree of dissociation H _n O

HqU z

3-1 θ is the volume of H 2 O in flue gas (m .j of fuel) _v 3 is the dissociation heat of H ₂ O to H ₂ ) kJ.m)

Q _vz is the thermal content of combustion air (kJ.j ^{3 of} fuel)

B .... thermal capacity of undissociated CO ₂ fraction in flue gas ^BV CO2 ⁽¹ - CO2 ' ^C co ₂

-3 -1 where c _nn is the specific heat of carbon dioxide (kJ.m.K) ^cu 2 thermal capacity of dissociated CO fraction? in flue gas, ie carbon monoxide CO ^CV CO ₂ · CO ₂ · ^C what where c _CQ is the specific heat of carbon monoxide (kj.m \ k 5

E .... thermal capacity of oxygen O formed by dissociation of CO, ^D = ^V CO2 · 2 ^ CO, · ^C O2

-3 -1 where c is the specific heat of oxygen 0 ₉ (kJ.m.K) of ²

G .... thermal capacity of undissociated H ₂ O fraction in flue gas ^{G = V} H, 0 ' ⁽¹ ' ^ ^H 2 ⁰⁾ · ° H, 0 of ₂ of

-3-1 where c _ŤT . is the specific heat H _n O (kJ.m.K) d ₂ U z

H ..... the thermal capacity of the dissociated H ₂ O fraction, ie hydrogen, in the flue gas

H = V _TT . <Á /

-3 -1 where c .. is the specific heat of hydrogen (kJ.m.K) ^H 2

J .... thermal capacity of oxygen produced by dissociation H ₉ 0

X .... thermal capacity of nitrogen

X = V. c 2

-1 where V _M is the volume of nitrogen in the flue gas (m .j of fuel) 2 _i c _M is the specific heat of nitrogen (kJ.m, ^{χ χ} ) ^W 2

Y .... O ₂ thermal capacity

-1 where V _n is the volume of oxygen in the flue gas (mj fuel) ^at 2

Example 1

Heavy fuel oil with a calorific value of 40 MJ.kg was used as fuel for firing the Portland clinker. At the same time, coal waste with a calorific value of 11.7 MJ was incinerated in the rotary kiln. kg 1, with a water content of 3% and a heat content of 55%. The weight of the coal-fired waste was 20% of the total fuel charge. This amount was determined using the above formulas, based on the chemical composition of the ash of both fuel types and processed raw materials to achieve the desired values of the silicate modulus Mg = 2.3, the aluminate modulus M ^ = 1.8, lime saturation S _Lp = 92. the combustion temperature was calculated to 1750 ° C. The produced clinker complied with ČSN 72 2121 for cement of class 325. This firing technology saved 23% of fuel oil compared to the traditional firing method.

Using the same fuels, but burned when the combustion air was enriched with 5% oxygen, an additional saving of 10% fuel oil was achieved.

Example 2

Coal waste with a net calorific value of 6.5 MJ.kg with an ash content of 70% was used for the experimental firing of Portland clinker in combination with heavy oil of the same calorific value as in the previous cases. With regard to the chemical composition of the ash fuels and the composition of the raw meal, the ratio of both fuels to 1 was set for the required values of the silicate module M _g - 2.6, the aluminate module M _A = 1.6 and the lime saturation S _Lp - 90. 2.5. The theoretical combustion temperature was calculated to be 1,720 ° C. The clinker produced corresponded to the required values for cement class 250 according to ČSN 72 2122.

Combustion of both types of fuels can be carried out either with one combined burner or in several burners burning individual fuels separately.

The invention can also be used for lime burning in rotary kilns.

AND

SUBJECT OF THE INVENTION

Claims (2)

SUBJECT OF THE INVENTION A method for firing cement clinker using coal waste, characterized in that in one and / or more burners of a burning unit, eg a rotary kiln, a noble fuel with a calorific value above 23 MJ.kg ¹ is simultaneously combusted with coal waste with a calorific value lower. than 17 MJ.kg 1 having an ash content greater than 30 wt.%, The amount is determined with regard to the chemical composition of ash from such wastes and noble fuel, together with the chemical composition of the cement raw mix depending on the desired value of the silicate modulus M _g = 1 8 to 3.0, an aluminate modulus M 1 - 1.5 to 4.0 and lime saturation S _Lp = 90 to 100 of the resulting Portland clinker, wherein the theoretical combustion temperature of the resulting fuel mixture must be greater than 1700 ° C. 2. A method for firing cement clinker according to claim 1, characterized in that the combustion air is enriched with oxygen.