Independent Temperature, Humidity Controls Optimize Kiln Performance
- Published: Tuesday, 01 June 2010 08:00
- Written by CP Staff
Now available in North America through a new Boonton, N.J., branch office of Stoke-on-Trent, England-based CDS Group, Envirocure temperature and humidity systems provide separate heat generation and water atomization to achieve desired humidity levels for block, paver, pipe and precast kilns or curing bays. CDS President Andrew Hall, relocating to New Jersey, notes that the systems' independent temperature and humidity controls yield efflorescence-free finished product exhibiting color and strength consistency. Moreover, appropriate Envirocure temperature and humidity combinations allow lower cement-content mix designs and/or higher supplementary cementitious materials usage for dry-cast concrete.
Independent control of temperature and humidity enables the producer to dial in suitable conditions for a given curing process. CDS Envirocure systems' separate heat-generation and water-atomization functions Û steam is not used to generate either heat or humidity Û permit temperature and humidity regulation to provide a noncondensing atmosphere. With adequate air circulation, controlled parameters thus ensure that cured-product strength and quality specifications are satisfied efficiently.
Envirocure benefits, i.e., reduced production costs, potentially lower cement content and/or cementitious substitute opportunities, nonefflorescence, and consistent product color and strength, are credited primarily to the systems' maintenance of optimum temperatures. Effective insulation, resulting in minimal heat loss, allows all heat of hydration to be used; and, little air escaping the system ensures a balanced airflow. Such air circulation creates constant conditions Û within 1_F and 95 percent relative humidity Û top to bottom and front to back throughout the kiln.
Envirocure's water feed with patented ultrasonic atomizers further facilitates control of humidity, which is monitored continuously and maintained at a high level, just below the dew point to produce a noncondensing atmosphere Û an anti-corrosion boon for plant machinery or any mechanical handling equipment that enters the curing cells. Due to lack of evaporation in the chambers' high-humidity atmosphere, product leaving the kiln upon completion of the curing cycle exhibits consistent strength, as well as a hard and nonfriable surface.
The mulitiple advantages of CDS Envirocure systems apply to both Individual Lane and Big Room models: differences exist only in their operation. Whereas an Individual Lane system entails loading units into a lane and waiting for the last one to enter the chamber before curing is initiated, the Big Room model accommodates product within a curing environment as it enters the Elevator and exits from the Lowerator, thereby reducing effective curing time. In the latter system, machinery is operating within the curing environment.
In view of the strengths of each model, CDS Envirocure II was designed to incorporate their advantages in a single system, providing the flexibility of controlled parameters in each kiln/lane to allow curing of various product groups at different temperatures and humidities. Accordingly, retaining wall, block, and pavers can be produced on the same shift and cured efficiently at differing temperatures and humidity levels.
Envirocure II enables users to input via MMI temperature (_F) and humidity (%RH) values for pre-set, ramp, dwell, and cooling phases. Thus, during a controlled ramp to curing temperature, dwell at temperature, and cooling, humidity is maintained at a desired level below dew point. A large volume of air circulation then ensures that all products within the kiln are exposed to identical curing conditions.
Enhanced performance of all Envirocure models, CDS engineers note, includes raising product temperatures from ambient up to the desired curing level by a direct gas-fired system that maintains temperatures precisely and efficiently to reduce overshoot and lag. Further maximizing efficiencies, heat of cement hydration is taken into account as the system constantly monitors temperatures within each cell. Consequently, during summer months, the CDS system's heat source may de-energize if temperatures are satisfied by ambient conditions and heat of hydration.
Additionally, humidity is injected only as needed when the level falls below a 95%RH setpoint. A fully recirculating system also ensures that product is maintained at constant conditions throughout the cell.