CS253054B1 - The method of firing cement clinker using coal waste - 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 of firing cement clinker using coal waste.

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

Brown coal and lignite are occasionally used for clinker firing, but only with calorific values and compositions that guarantee, in the dried state, combustion temperatures at the level of the combustion temperature of black coal with the stated calorific value of 23 MJ.kg.

The disadvantage of the current situation is the lack of high-quality fuels and their ever-increasing price. The possibility of partial replacement of these fuels with black or brown coal with a lower calorific value causes an increase in specific heat consumption and thus absolute fuel consumption, notwithstanding the fact that the share 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 certain additional costs for their transportation, processing and drying, compared to the use of the original single-component fuel.

The above-mentioned shortcomings are eliminated by the method of firing cement clinker, the essence of which is that in one and/or more burners of a firing unit, e.g. a rotary kiln, noble fuel with a calorific value above 23 MJ.kg is simultaneously burned with coal waste with a calorific value below 17 MJ.kg with an ash content above 30%, the amount of which is determined with regard to the chemical composition of the ash from these wastes and noble fuel together with the chemical composition of the raw cement mixture depending on the required values of the silicate module Mg = 1.8 to 3.0, the aluminate module M^ = 1.5 to 4.0 and the lime saturation S _Lp = 9é to 100 of the resulting Portland clinker, while the theoretical combustion temperature of the resulting fuel mixture must be higher than 1,700 °C.

The method in question makes it possible to partially replace noble fuels such as heating oil or natural gas with lower-value solid fuels, e.g. coal waste. Even such a partial replacement of noble production fuels represents a significant reduction in production costs during the firing of cement clinker.

The invention will be explained in more detail below with examples of its practical implementation.

When determining the amount of inferior fuel that can be burned without affecting the quality of the resulting product, the following relationships are used:

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 calcium oxide CaO content in % by weight.

S is the content of silicon dioxide SiC^ in wt.%.

A is the content of aluminum oxide AJ^Og in % by mass.

F is the content of iron oxide F®2°3 ⁱⁿ % ^ ^mot · where the oxide contents are related either to the clinker or to the raw material.

Theoretical combustion temperature ^Q n ^{+ Q} C02 ^{+ Q} H2O ^{+ Q} VZ

T. _

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

_Q is the chemically bound heat of dissociated carbon dioxide CO^ (kJ.j ¹ fuel)

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

-* Λ

3-1 ^In CO2 °kj ^ein CC>2 in flue gas (m . j fuel) _3

Q is the dissociation heat of C0 ₉ to CO (kj.m )

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

HQU from

3-1 θ is the volume of H^O in the flue gas (m .j of fuel) _v _3 is the heat of dissociation of H ₂ O to H ₂ )kJ.m )

Q _vz is the heat content of the combustion air (kJ.j ³ fuel)

B .... heat capacity of the undissociated portion of CO ₂ in the 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 heat capacity of the dissociated portion of CO? in the flue gas, i.e. carbon monoxide CO ^CV CO ₂ · CO ₂ · ^C co where c _CQ is the specific heat of carbon monoxide (kj.m \k 5

E .... heat 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 ) z ²

G .... heat capacity of the undissociated portion of H ₂ O in the flue gas ^{G = V} H,0 ' ⁽¹ '^ ^H 2 ⁰⁾ °H,0 z ₂ z

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

H ..... heat capacity of the dissociated portion of H ₂ O, i.e. 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 .... heat capacity of oxygen formed by dissociation of H ₉ 0

X .... heat capacity of nitrogen

X = V . c 2

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

Y .... heat capacity of oxygen O ₂

-1 where V _n is the volume of oxygen in the flue gas (m .j fuel) ^u 2

Example 1

For the firing of Portland clinker, heavy fuel oil with a calorific value of 40 MJ.kg was used as fuel. At the same time, coal waste with a calorific value of 11.7 MJ. .kg 1, with a water content of 3% and an ash content of 55% was also fired in the rotary kiln. The weight of the burned coal waste constituted 20% of the total fuel charge. This amount was determined using the above-mentioned relations, based on the chemical composition of the ash of both types of fuel and the processed raw materials to achieve the required values of the silicate module Mg = 2.3, aluminate module M^ = 1.8, and lime saturation S _Lp = 92. The theoretical combustion temperature was calculated at 1,750 °C. The produced clinker complied with ČSN 72 2121 for cement class 325. This firing technology resulted in a saving of 23% of fuel oil compared to the traditional firing method.

When using the same fuels, but burning them with combustion air enriched with 5% oxygen, an additional saving of 10% of heating oil was achieved.

Example 2

For the experimental firing of Portland clinker, coal waste with a calorific value of 6.5 MJ.kg and an ash content of 70% was used in combination with heavy oil with the same calorific value as in the previous cases. With regard to the chemical composition of the fuel ash and the composition of the raw meal, the ratio of both fuels was determined to be 1:2.5 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 using the above-mentioned relations. The theoretical combustion temperature was calculated to be 1,720 °C. The produced clinker corresponded to the required values for cement class 250 according to ČSN 72 2122.

Combustion of both types of fuel can be carried out either with one combined burner or in multiple 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.