PCME - Passionate about Particulate

The metals industry is a core focus for PCME’s business, with extensive experience in primary and secondary aluminium smelters, integrated steel mills and steel mini mills driving the continuous development of monitoring solutions to best meet the demands of industry. Experience gained from over 5,000 applications in the metals industry alone gives PCME a comprehensive understanding of the potential issues facing particulate monitoring for the aluminium industry, in particular:

• Recognising the value of filter performance optimisation for calciner abatement plant, to minimise product loss and maximise filter and process efficiency
• Harsh and dusty environments require dependable and rugged sensor operation, where reduced sensor maintenance requirements, reduced sensitivity to sensor contamination, and a range of durable sensor options for challenging stack conditions are of significant benefit to plant operators
• Networked multi-channel particulate monitoring systems for the large, multi-chamber bagfilters used after milling and electrolytic reduction plant

PCME offer approved (TUV & MCERTS) systems for particulate measurement, filter leak monitoring and filter performance monitoring, depending on the plant specific requirements which are specified in close consultation between plant operators and PCME. Aluminium plant typically demands monitoring on multiple emission points across milling, refining, reducing and casting operations, which can be addressed with a networked multichannel system. By offering a range of measurement technologies in reliable and rugged instruments, PCME are able to offer a full range of solutions to meet and often exceed legislative compliance, and significantly improve the operation of filter plant including a reduction in filter maintenance requirements.

As knowledge and awareness increase in the environmental and health concerns associated with metallic particulates, regulators are increasingly focusing on operators of metals plant to enforce lower emissions limits and more strict compliance programs. With a history of establishing, developing and maintaining strong partnerships within the metals industry, PCME bring extensive experience for assisting plant operators to both minimise emissions and improve the operation of filter plant.

Refining

Refining raw bauxite to alumina in primary smelting produces high concentrations of particulate emissions at several stages of the process, particularly from milling and calcining plant. As the particulate matter is of value and is typically collected to recycle into the process, plant operators benefit from maximising collection efficiency and being able to continuously monitor the performance of filtration plant, for example for failing ESP plates or broken filter bags, enabling preventative maintenance and minimised process down time.

For example, fugitive emissions from the crushing of bauxite ore in ball mills are typically abated with large multi-compartment bagfilters, while calciner plant emissions are abated with large electrostatic precipitators, or bagfilters on more modern plants. In each of these cases, the particulates collected in the filtration plant are of value and are collected for recycling back into the process.

Reduction

Both primary and secondary aluminium smelting operations produce particulate emission concentrations of 150-500 mg/mg³ before abatement (depending on the specific process), and 1-20 mg/m³ after abatement. Particulate emissions from various stages in the process include alumina, carbon (from anode dusting), cryolite, aluminium fluoride, calcium fluoride, and ferric oxide, with fluoride particulate emissions at the forefront of regulators’ concerns.

Reduction cell and anode baking furnace emissions have commonly been abated with wet scrubbers (e.g. spray driers) and electrostatic precipitators, although due to the efficiency of the fluoride absorption method via a fluidized bed of alumina, this is increasingly prevalent. High efficiency bagfilters are used to capture alumina downstream of the fluidized bed, allowing the recycling of the fluorides and use of the captured alumina as feedstock for the reduction cells. The benefits of comprehensive filter monitoring and management are clear, with gains in terms of process optimisation and reduced costs alongside assured regulatory compliance.

Secondary aluminium smelting, typically with reverberatory furnaces, as well as other operations such a lance fluxing, rotary injection, tapping and casting operations also produce particulate matter emissions including metallic fluorides, which are abated most commonly with large multi-compartment fabric bagfilters.



 

Sufficient minimum detection level for highly abated emissions:

PCME’s ElectroDynamic™ Probe Electrification technology has a minimum detection level (0.1mg/m³) suitable for highly abated emissions, such as those found after bagfilter plant in Aluminium Plant, including QAL1 approved instruments with certification range 0-15mg/m³ for Emission Limit Values as low as 10mg/m³) . ProScatter™ Forward Scatter instruments such as PCME QAL 181 are suitable for lower concentrations of <0.1mg/m³, and are also certified and compliant to the most demanding European (MCERTS and TUV) and US EPA (PS-11) standards. For monitoring emissions after electrostatic precipitators, PCME’s range of DynamicOpacity™ Ratiometric Opacity instruments are also available with TUV performance approvals.

Contamination Detection and Tolerance:

Short Circuit and Contamination Detection
With traditional Probe Electrification type instruments, performance can be compromised by contamination of the sensor probe insulator by conductive particulate matter. Over time, this build up can allow short circuit of the sensor probe via ‘bridging’ of the insulator, which is of particular concern in Aluminium Plant applications where conductive particulate matter is prevalent. PCME’s ElectroDynamic™ range of instruments includes a patented probe rod contamination check feature, which provides operators with a pre-warning check of possible probe rod short circuit, enabling predictive sensor maintenance scheduling, lower down times and confidence in signal integrity (see PCME STACK 990).

Tolerance to Contamination
PCME’s unique and patented ElectroDynamic™ Probe Electrification technology allows sensors to operate normally with significant contamination build-up on the sensor rod, avoiding the signal drift issues associated with traditional probe electrification type instruments and offering greatly reduced maintenance requirements. Additionally, PCME’s patented insulated sensor rod option offers unrivalled performance in high humidity (non-condensing) applications.

DynamicOpacity™ Ratiometric Opacity instruments are often used to replace standard Opacity instruments which require extensive maintenance and servicing time, as they offer the significant advantage of the ratiometric measurement being unaffected by lens contamination. The instruments can provide calibrated measurement with lens contamination exceeding 90%, and are therefore highly reliable with extended maintenance intervals (see PCME STACK 602). These instruments are particularly suited to electrostatic precipitator performance optimisation after calciner abatement plant, as they are able to continue operating reliably in the humid, contaminating conditions.

High Temperature Operation:

PCME instruments include medium and high temperature options up to 800°C, to handle the harsh, aggressive temperatures found in Aluminium Plant applications, particularly after exhaust gas combustion. High grade ceramics combined with heat shields and heat sinks allow the sensors to operate normally and reliably under temperatures far in excess of standard type sensors.

Variable Speed Fans & Flue Gases:

As variable speed fans are common in ducting as part of emissions exhaust systems in Aluminium Plant, PCME’s ElectroDynamic™ instruments with reduced sensitivity to variations in flue gas velocity provide a significant performance advantage over standard probe electrification type instruments. PCME’s ProScatter™ Light Scatter instruments have no velocity dependence so offer a further option depending on the application conditions.

Network Integration:

Aluminium Plant typically requires instrumentation across several emissions sources. PCME sensors can be networked into one central control unit, integrated with existing plant DCS/SCADA systems, and provide Ethernet connectivity for plant-wide LAN integration.

Quality Assurance:

Stricter compliance programs and more rigidly enforced emission limits within the metals industry mean that operators require an increased level of quality assurance, and confidence in their emissions monitoring systems to operate correctly and also minimise emission limit excursion events. PCME offer systems approved to the latest MCERTS & TUV standards, with manual or automated zero and span / reference drift checks for ongoing quality assurance, and other system self-checks such as short circuit, probe contamination and network communication checks to provide confidence in data integrity and to facilitate predictive maintenance scheduling.