ADVANCEMENT IN AIR & PROCESS GAS FLOW MONITORING IN CEMENT PLANTS FOR PROCESS OPTIMIZATION

 One of the essential foundational industries for the growth of infrastructure and building is the cement industry; in 2021, the globe produced about 4.4 billion tons of cement. China is the world’s largest cement producer, with over 55% of the global capacity; India comes in second, with over 7% of the global capacity.

Following the COVID-19 epidemic, there was an abrupt increase in demand for both urban and rural infrastructure expansions worldwide, primarily in developing nations. Long-term demand for cement products will result from initiatives like India’s Smart City project, which will push current cement plants to greatly upgrade their technological capabilities in order to optimize energy and cost.

Among all industrial sectors, the cement industry is one of the ones that uses the most energy. Between 40% and 60% of industrial expenses are attributed to energy use. In addition, the cement sector accounts for 5% to 8% of global emissions of CO2 produced by humans. Today’s cement plant operators will prioritize efficiency and optimization due to the rising demand, which will primarily rely on the precise and repeatable measurement of several process parameters like temperature, pressure, flow rate and level, etc.

In the cement industry, process gas flows are typically calculated using temperature and pressure in relation to the speed and power consumption of fans and blowers. However, this is an assumption that creates significant uncertainty regarding the real gas flow rate and energy consumption of prime mover, such as fans and blowers.

The following processes require the best possible control over air and process gas flow monitoring in order to improve cement quality overall, efficiency, and cost optimization:

1. PREHEATER PROCESS EXHAUST GAS FLOW RATE MEASUREMENT:

Before the raw mix is put into the rotary kiln in a cement production facility, it is heated in cyclone preheaters, which also remove water and carbon dioxide from the mixture. The stability of the calcining temperature and the quality of the cement clinker in the kiln are directly impacted by the caliber of the preheater in a cement plant. The ID Fan downstream can be fine-tuned for optimal management of the O2 content of the kiln off gas by measuring the exhaust gas flow rate in the downcomer.

The measurement of exhaust gas flow is often difficult because of the duct’s enormous diameter, the high concentration of dust, and the high temperatures (between 350 and 400 degrees Celsius). Velocity is typically measured momentarily using a Pitot tube with large uncertainty for cross-checking, which hinders effective process management.

2. CLINKER COOLER AIR FAN FLOW RATE MEASUREMENT:

A crucial component of the clinker manufacturing line, the clinker cooler provides hot air for the rotary kiln and preheater system as well as aids in cooling and transporting the hot clinkers that are discharged from the kiln. It is essential for decreasing the amount of coal and power used, raising the temperature of secondary and tertiary air, and enhancing the rate of heat recovery since it is the first piece of equipment where high-temperature clinker releases heat.

Two ways that a good clinker cooler can assist cement plants in reducing energy consumption are by increasing the cooling efficiency and lowering the power consumption of the clinker cooler itself, and by increasing the heat recovery rate, which can lower the amount of coal used in the rotary kiln and preheating systems. In order to achieve cooling efficiency and energy savings with a higher cooling rate concerning feed rate adjustment, clinker cooler grate air fan effective management is essential. For a clinker cooler to operate as efficiently as possible, continuous cooling air flow rate measurement is crucial.

Because of the high concentration of clinker dust and high abrasion rate, measuring a cooler air fan is a difficult operation. Strong flow sensors that are resistant to severe abrasion are required. This application’s flow solution is currently restricted, and its life expectancy is only 1–6 months.

3. AQC BOILER & PHP PROCESS GAS OUTLET FLOW MEASUREMENT:

The heat produced by the rotary kiln preheater (PH) and the hot gases from the AQC exhaust are used to create power in waste heat recovery (WHR) power plants, which are situated in cement factories. Waste heat recovery systems (WHRS) use steam turbines to recover heat energy from hot waste gas that is sent to boilers for power generation (in this case, electricity) and after quenching chambers (in this case, clinker cooler and preheater boilers in rotary kilns. Usually, this waste heat can be used for power generation applications to meet the cement plant’s 20–30% power need, which results in a significant reduction in the overall cost of production.

Effective management of pH and AQC A flow measurement device that is appropriate for high temperatures and abrasion resistance design is required by the boiler in order to ensure an accurate and dependable gas flow rate at the intake or output.

4. PRIMARY AIR FAN FLOW MEASUREMENT IN POWER GENERATION BOILERS:

In addition to AQC & PH Waste heat recovery boilers, a captive coal power plant is erected in the cement plant to provide additional electricity needs. It’s critical to keep an eye on the boiler’s primary airflow in order to maintain the ideal stoichiometric air-to-fuel ratio and achieve effective combustion. It is necessary to have a primary air flow measurement that is accurate, dependable, and low-maintenance. It should also have a minimal pressure drop.

5. PROCESS & FLUE GAS FLOW MEASUREMENT IN EXHAUST STACK:

For the purpose of maintaining control over emission criteria, the pollution control authority must monitor the exhaust process flue gas from the boiler and clinker cooler. In order to achieve high thermal efficiency, enhance ESP performance, minimize emissions of dangerous pollutants, and provide helpful information on optimizing mass balance, this requires accurate and dependable flow measurement technologies.

6. COMPRESSED AIR MEASUREMENT FOR UTILITY CONTROL AND CONSERVATION:

In cement plants, compressed air is a necessary resource for the effective operation of pneumatic equipment used in packing factories. Its other uses, however, require monitoring because it is an invisible energy source — one horsepower (HP) of electrical energy is needed to produce four standard cubic feet of compressed air.

AN ACCURATE AIR & GAS FLOW MEASUREMENT IN CEMENT PRODUCTION HELPS IN:

• Reducing Blower (ID/FD Fan) power consumption i.e., energy saving
• Controlling the accurate and repeatable operation of kiln & improving clinker production quality
• Improves energy efficiency of Clinker cooler fan & energy conservation

MAJOR CHALLENGES IN EXISTING FLOW MEASUREMENT SOLUTIONS FOR THE ABOVE APPLICATIONS:

• High-pressure drop means energy loss
• Lower turn-down ratio implies limited operational range and leakage insensitive.
• Lower accuracy & measurement resolution implies limited efficiency & performance analysis
• Clogging and high wear factor
• High cost of installation & needs frequent maintenance.

OVERCOMING ABOVE CHALLENGES BY ADVANCE PROVEN CALORIMETRIC (HEAT DISSIPATION) TECHNOLOGY:

The technology of Insertion Thermal Mass (Heat Dissipation) Flow Meters is advancing these days to overcome the drawbacks of the traditional pitot tube or annbar differential pressure-based flow measurement methods now in use.

NSERTION THERMAL MASS FLOWMETER:

WORKING PRINCIPLE:

The fundamental principle of thermal dispersion from a heated element to the ambient medium (such as air or gases) underlies the operation of thermal mass (calorimetric) flow meters. The velocity, density (temperature and pressure), and properties of the medium all have an impact on this. The mass flow and temperature differential, ∆T, determine how much energy is required.

Gas passing via two RTD Pt-100s two Heaters: one (Th) and one (Tref). The reference sensor’s (middle temperature) and the heater sensor’s temperature differential (over temperature) are continuously adjusted. King’s Law states that when the mass flow rate increases, the heater sensor’s cooling effect increases as well, requiring more power to keep the difference temperature constant. As a result, the gas mass flow rate and the heater power are proportionate.

ADVANTAGES OF INSERTION THERMAL MASS FLOW METERING TECHNOLOGY AGAINST CONVENTIONAL FLOW METERING:

• Pipe sizes suitable 15mm to 10 metres
• Easy Installation, orientation & rugged design with customized sensor material design
• Working temperature upto 40⁰⁰C & 16barg or higher can be achieved
• Better accuracy < ±2%RD of mass flow rate
• Highest turn down ratio 100:1 or better, too sensitive throughout flow ranges.
• No pressure drop saves energy (pressure) loss
• Versatile & Cleanable sensors (auto-purging) design
• Can be used with too low upstream straight length with special installation procedure
• Low cost of ownership against other flow technology

CONCLUSION:

The main components of a cement plant are large ducts with blowers (FD & ID Fans). Conventional flow measurement uses differential pressure sensors as primary elements, such as average pitot tubes, orifices, and aerofoils, which are prone to clogging, insensitive to changes in flow velocity, and result in significant pressure drops with lower accuracy. It has now been shown that using differential pressure sensors against the latest development in heat dissipation technique — insertion thermal mass flow — is generally uneconomical when compared to inserting thermal mass flow (heat dissipation technique) metering.

Current research is being done to develop more materials that are compatible with hot gas that has high abrasion and heavy dust concentration. These materials will meet the majority of application needs in cement plants, with the exception of a few that have temperature restrictions up to 500°C. Conventional technologies continue to dominate the industry, with operating temperatures remaining above 50⁰⁰C. I hope this will assist operators of cement plants in seeing the advantages of utilizing modern technologies in place of traditional flow measurement.

AUTHOR:

Mr.Manish S Patel, A Chartered Mechanical Engineer with more than 24 years rich experience in process industries especially in flow measurement with a wide range of applications.

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