Steam is today’s utility player in the industrial energy arena. Steam power generation is so essential to industry that it comprises 83% of the total energy used by the pulp and paper segment (57% for chemicals and 42% for refining). Steam is ubiquitous because it’s industry friendly. It’s intrinsically safe, flexible, economical, aseptic and environmentally benign.
It is not an uncommon practice in this day and age for plants using steam power generation to employ a waste heat and/or condensate recovery process to reduce energy losses and capture valuable condensate. The use of instrumentation technology that cannot adequately or reliably address the control aspects of these processes can inhibit the effectiveness and overall return on investment in these systems or expose hardware to unnecessary damage.
Magnetrol® has produced the “Optimizing the Steam Generation Cycle and Condensate Recovery Process for Profit” kit to help improve plant efficiency. This kit includes a white paper that identifies key areas where cost-effective instrumentation solutions can improve control. Here is an excerpt from the white paper on the challenges for optimizing boiler and steam drum level control:
The Steam Power Generation Cycle
Steam power generation and condensate recovery systems can vary in complexity depending on the steam end usage and process requirements, e.g., steam for electricity generation or to support a paper mill operation versus that for a small to mid-size specialty chemical process operation.
Figure 1, below, is a simplified diagram depicting a basic steam power generation cycle, scalable to virtually any plant requirement whether incorporating a fire tube or larger water tube type boiler. It should suffice to highlight critical areas in the cycle where addressing level control concerns can have a profound impact on efficiency, reliability and maintenance.
At the heart of the system is the boiler/steam drum. Regardless of size, its primary functions are as follows: to provide ample surface area (based on steam needs) for the efficient separation of water and steam; to provide storage capacity to meet immediate boiler feed water requirements or minimize the effects of the introduction of boiler feed water on the steam generation process; and to facilitate the introduction of chemicals for treatment purposes as well as the removal (blowdown) of impurities.
A boiler, whether fire or water tube, presents an extremely dynamic environment with respect to level control regardless of the control strategy— single-, two-, or three-element. The common denominator in each of these strategies is the level measurement itself. Applying a technology that improves on this portion of the equation will most certainly aid in allowing the boiler/steam drum to better serve its primary purpose of efficiently separating water and steam. This becomes more pronounced when fluctuations in demand can have dramatic effects on an instrument’s performance due to “shrink” and “swell” issues as a result of pressure changes. In larger-scale steam production such as that required for commercial power generation (water tube boilers), disruptions in boiler/steam drum level control can have adverse effects on the natural circulation of the process and a plant’s ability to respond to market demand.
Level technologies historically used on boilers rely on inference or buoyancy to determine the level. This in itself leaves them vulnerable to process dynamics (specific gravity, pressure, temperature, etc.) or limits their ability to precisely manage the level for improved fuel economy. Although corrections can be applied to mitigate the effects, the variables that need to be accounted for increase the level control’s installation, hardware and calibration complexity, which has the unintended consequence of introducing new avenues for error. Eliminating potential sources of error (including human error) as related to an instrument’s fundamental technology is the first step in optimizing boiler/steam drum level control.
By identifying key areas in the steam power generation cycle where efficient and reliable instrumentation solutions offer a tangible return on investment, an operation can reduce heat rate, environmental impact, fuel and water consumption, water treatment and maintenance costs in commercial and heavy industries where steam generation is essential to the production processes. To learn more, visit steamgen.magnetrol.com.