CONTENTS

1.0Introduction

2.0Pulverizer Performance Guarantees

3.0Pulverizer Testing

4.0References

5.0Prerequisites

6.0Procedure

7.0Attachments

1Introduction

Performance monitoring guidelines for a steam generator should address the various equipment that affects steam generator performance degradation in a major way. The guidelines detailed in this document covers pulverizers.

1.1Pulverizers and Burner Equipment

Combustible loss-on-ignition from fly ash samples should be determined regularly and reasons for excess carbon carryover identified. Fly ash samples need to be collected from a representative location and the difference between left and right side of the boiler should be tracked. Airflow at mill inlet and outlet should be initially checked to ensure proper flows and distributions and to eliminate pulverizer spillage. Mill performance should be monitored using parameters such as mill fineness, mill power, measured air and coal flows, coal spillage, coal grindability and moisture in coal. Secondary air distribution should be checked where practical to ensure proper airflow distribution and to maintain proper stoichometery in the combustion zone.

1.2Boiler

Boiler oxygen analyzer systems should be investigated for proper location and accuracy. Single point monitoring is often considered adequate for operating the boiler but this can result in operation at high/low level of excess air. Boiler casing leakage can adversely effect the value of oxygen percentage being maintained. All ductwork and expansion joints should be checked for possible leakage.

1.3Air Heaters

Air heater leakage levels should be determined by using data base obtained from proper grid analysis. Excessive leakage results in increased fan power consumption, greater potential for cold end corrosion and potential load curtailment due to insufficient combustion air. Tri sector air heater performance has been a major contributory factor in the degradation of steam generator performance and experience on automatic leakage control system – (ALCS), also has not been very satisfactory.

1.4 Fans

The actual position of damper blades should be checked against control room or actuator readings. A partially open damper will reduce fan capacity, potentially affecting the unit output and waste energy.

1.5 Balancing Coal Flows To Improve Boiler Performance

Uneven distribution of pulverized coal to burners operating in parallel adds to combustion problems such as flame blow out, excessive NOx formations, low burnout, combustion oscillations and uneven combustion across the furnace, with subsequent poor plant performance. It has been a common engineering practice to balance the two phase flowprimary air and pulverized coal through parallel piping by sizing orifice plates for each pipe based on clean air tests. Flow resistance is equalized under clean air conditions, but when coal is added to primary air, the physical characteristics of the flow regime change. The distribution through parallel piping shall no longer be balanced especially if it consists of different lengths, bends, elevations and orifices. This technique as described in the following pages can play a very vital role in realizing the full potential of combustion system. It offers an alternative feed back on various measurements related to a pulverizer system.

2Pulverizer Performance Guarantees

The scope of performance Guarantees envisaged in NTPC specifications is very comprehensive and invariably these tests are carried out religiously to demonstrate the design margins and operating flexibility. Typically, the following parameters are guaranteed for milling plants.

a)Pulverizer output, t/hr at a specified level of fineness

b)Power consumption kW/t of coal at specified level of fineness

c)Wear parts guarantee

d)Capability to operate two adjoining pulverizers at 50% load without oil support

e)Turn down ratio

Performance tests are not generally conducted with design coal, which brings into focus the correction curves furnished by the mill manufacturer. Sanctity of correction curves needs to be confirmed using a sound database established by the utility, whereas utility normally depends on the mill manufacturer for test instruments for demonstration of basic guarantees. It makes sense to buy test equipment as a part of the equipment package along with other tools and tackles to establish an effective database even after completion of acceptance testing. Application of correction curves