As we’ve discussed in previous articles, X-ray fluorescence (XRF) is an analytical technique for learning the exact elemental composition of materials. It has many applications in the mining industry. Another important elemental analysis technology for the mining industry is Prompt Gamma Neutron Activation Analysis (PGNAA), which is well suited for the niche market of cement production both by itself and in combination with XRF.
So what is PGNAA?
PGNAA works by bombarding sample material with neutrons. PGNAA online analyzers require a source of neutrons for their analysis technique. Historically the most reliable and safest source of neutrons has been the radio-isotope Californium-252. However, with a degree of complexity, neutrons can be electrically generated with a specialized compact linear accelerator called a Neutron Generator. Neutrons interact with elements in the sample, which emit secondary prompt gamma rays. These gamma rays are collected and measured with a high resolution gamma ray spectrometer. The gamma ray spectrum is analyzed to determine information about specific elements. Like XRF, PGNAA relies on unique elemental signatures. In this case, each element emits a characteristic gamma ray signature as it returns to a stable state. Each element also has a different tendency to interact with neutrons; those with a high tendency are measurable. The element must emit a gamma ray within the energy window being analyzed. The element must also have enough atoms present in the sample that the probability of that element being impacted by a neutron is sufficient enough to be detected (this is a function of the amount of material being analyzed and the percentage of the element in that sample).
You can read more about PGNAA technology here.
What makes PGNAA particularly suited for cement analysis? PGNAA is a comprehensive analysis technique.
PGNAA analyzers are situated directly on the conveyor belt and penetrate the entire raw material cross-section, providing minute-by-minute, uniform measurement of the entire material stream, not just a sample. Surface analysis technologies such as XRF, X-ray diffraction (XRD), and other spectral analysis technologies measure limited depths and surface areas that may not be representative of the entire amount of material on the belt. With PGNAA, sample errors are reduced, and the high-frequency of analysis helps reduce variation in material quality.
PGNAA improves stockpile and raw mix control.
Cement producers who must meet increasingly stringent customer and regulatory requirements are turning to PGNAA cross belt analyzers for elemental composition data to improve quality control, process efficiency, energy savings and waste reduction. Cement raw materials must be carefully monitored and controlled to ensure the quality and conformity of the final product, concrete. Variances in raw material quality or improperly blended materials can result in faulty concrete and potentially dangerous and expensive construction issues such as building and bridge failures. One of the most significant ways an online analyzer can help a cement producer is to save energy costs and reduce raw material waste. A stable cement manufacturing process with the correct chemistry takes much less energy to run than a highly variable process. The more variability in the raw materials, the more fuel the producer must use to get the materials to “react chemically” in the kiln to make cement. If a producer doesn’t know the chemistry of his raw materials well enough, many times they will err on the safe side and waste materials that have a questionable chemical composition. An online analyzer helps avoid waste by quickly and thoroughly determining the quality of raw materials.
PGNAA provides online analysis.
Traditional cement plants conduct material analysis by taking samples from a transfer tower to a lab for analysis. PGNAA analyzers are online systems installed on the conveyor belt, so materials are measured continuously and in real time with much better representation. Errors associated with off line sampling are eliminated and the raw materials can be sorted and blended correctly. Eliminating the tower also reduces construction and maintenance costs and downtime from tower issues. PGNAA data can be combined with XRF lab results for improved process optimization. Mining lab software is available that helps keep the PGNAA online analyzer “aligned” or calibrated to the off-line, laboratory X-ray analyzer system so that both are synchronized with each other. Read the story of a cement processing plant that installed a cross belt analyzer with PGNAA technology to optimize their operational efficiency and product quality.