Comparative Properties of Bituminous Coal and Petroleum Coke as Fuels in Cement Kilns

Bituminous coal has been in use as fuel in cement kilns for a long time. With coal costs continuously rising, cement plants have been looking for alternative less expensive fuels. Petroleum coke presents a viable alternative because of its lower cost since it is a byproduct of the refining process. It has a high heat value and low ash content, which favor its use in cement kilns. However, petroleum coke presents some challenges, such as high sulfur content and poor grindability, compounded by the need to grind it finer due to a low volatile content.

Comparative-Properties-of-Coal-and-Petcoke

The following table provides a comparison between bituminous coal and petroleum coke with respect to their characteristics and operational and emission aspects. The comparison is on a very broad basis and an evaluation is required for each specific coal and petcoke origin.


COMPARISON BETWEEN BITUMINOUS COAL AND PETROLEUM COKE

 

 

Coal

Coke

Comments

Mitigation

Measures

EMISSION

 

SO2 emission: (Depends on % S in fuel and alkali content in the raw mix)

Low

High

Typically Petroleum coke comes with 4 – 7% Sulfur content.

Lime injection.

Alkali balance.

Process strategy.

 

NOx emission:

(Petroleum coke is low in volatiles and the combustion occurs at a higher temperature)

Low

High

High flame temperature in the kiln generates higher thermal NOx

Multi staged combustion technique and SNCR (Selective Non Catalytic Reduction) technology.

 

OPERATION

 

Coating formation and preheater plugging

Low

High

High sulfur increases circulation of volatiles and potentially cause plugging in preheater

Alkali balance and operational strategy

Sulfur bypass

Grinding load

Low

High

Petcoke is hard to grind and needs finer grinding

No remedy

However, lower fuel requirement due to higher heat value.

Raw mix design

Higher ash levels

Low in ash

Raw mix needs to be adjusted for ash absorption

 

SAFETY

 

Fire and explosion hazard

high

low

Low volatile content makes petcoke safer to handle

Inerting systems and explosion vents are required.

CLINKER QUALITY 

 

SO3 content in clinker

low

high

Permissible SO 3 content in clinker limits the use of some petcokes

 

CHARACTERISTICS

 

% Ash Content

14 – 20

0.5 – 1.0

Petroleum coke is superior in heat content due to lower ash content.

 

% Fixed Carbon

55 – 60

82 - 87

Higher carbon content gives higher calorific value (CV).

 

% Sulphur

0.5 – 1.0

4 - 7

Creates emission of SOx and Operational problems.

Please refer to point A1 and B1

Gross C. V. kcal/kg

6000 - 6200

8000 - 8200

With higher calorific value less amount of Petroleum coke is required.

 

Hardness – HGI

The lower the HGI, the harder to grind.

50 – 55

35 - 40

Higher grinding (electrical) energy due to lower HGI.

 

% Volatile matter

22 - 27

7 - 8

Petroleum coke is a slow reactive fuel difficult to burn, making it a less of a fire and explosive hazard.

Special burner for petcoke. High flame momentum kiln burner.

Finer grinding.

Longer retention time in Pre-calciner.

 

 

           

                        

Petroleum coke is a viable alternative fuel to Bituminous Coal provided the challenges associated with it are properly addressed.

The quality of Petroleum coke varies from source to source. Depending on the refining process, various types of Petroleum coke are produced.

To ensure a successful operation, a detailed study based on the characteristics of the raw material and Petroleum coke to be used is required.

Additional investment may be envisaged for incorporating technology that supports use of Petroleum coke as fuel and for controlling environmental emission levels.

The use of petroleum coke may be limited by its high sulfur content. Technological measures such as finer grinding, pre-calciners designed to have a higher retention time, an external combustion chamber before the calciner, a special high-momentum kiln burner, etc. will help to effectively utilize Petroleum coke.

Based on the quality of Petroleum coke, typically a mixed fuel firing is designed. The percentage of Petroleum coke is determined based on quality and operational trials.


This article was contributed by Jagrut Upadhyay, Senior Process Consultant, and Narayana Jayaraman, Director – Technical Services at PEC Consulting Group.

View additional feature articles under PublicationsContact Us