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Full-Scale Utility Boiler Ash and Deposit Sampling

The EERC has participated in collecting both online and off-line ash samples at various utilities to compare bench- and pilot-scale results with full-scale units. Sampling can involve collecting coal, convective pass deposits, entrained ash, fly ash, slag (cyclone-fired boilers), and hopper ash for detailed characterization using advanced inorganic analysis techniques.

During online testing, various equipment is used to gain as much knowledge of the conditions of the boiler system as possible. Temperature profiles are obtained by a high-velocity thermocouple (HVT); an infrared temperature monitor records temperature fluctuations during the course of the testing; and gas analyses are used to measure important gas components such as O2 and SO2. Specially designed cooled probes are used to collect entrained ash and ash deposits.

Long-Duration Deposition Probe

The long-duration deposition probe (LDDP) was designed and fabricated to collect long-term (from days to weeks) deposits from utility boilers to investigate the formation and strength development mechanisms of calcium sulfate-rich deposits. The LDDP consists of a deposition probe attached to a probe carriage which moves on translation rails housed in a pressure shell rated to 5 psig. An air-driven motor supplies the drive to move the probe in and out of the furnace. Deposits are collected on sacrificial coupons made of materials representative of boiler tubes attached to the end of the probe and maintained at a skin temperature of 1000°F by air cooling. The probe can be extended approximately 5 ft into the boiler.

During sootblowing, the probe is retracted into the pressure shell to protect the deposit forming on the coupon. While the probe is retracted, the deposit is kept hot by an electric furnace installed at the front of the pressure shell to minimize thermal shock to the deposit. A data acquisition system controls and monitors the temperatures and airflows. An on-site computer can record operating data onto a computer disk or relay the data to another monitoring site. Still video images of the probe deposit as it is being formed can be taken by a shell-mounted TV camera.

Entrained Ash Particulate Collection Probe

The entrained ash particulate collection probe was designed and fabricated to sample entrained ash from utility boilers at or near isokinetic rates. The probe has been successful in obtaining samples from the convective passes of various types of boilers, including a pressurized cyclone-fired boiler. Water cooling of the probe allows sampling collection time of up to 2 hours. The collected ash is size-segregated in a four-stage multicyclone system manufactured by Aerotherm. The Aerotherm source assessment sampling system consists primarily of three cyclones and a final filter housed in an oven to maintain the temperature above the acid dew point of the gas stream.