Winter heating in sewage treatment plants

The insulation measures of sewage treatment plants were built and laid out earlier in the cold regions of North China. In some areas, since last year, the provincial environmental protection department has been promoting "wearing clothes and hats" in sewage treatment plants, requiring thermal insulation and capping of biological ponds, as well as warming of sewage. In response to this requirement, sewage plants in some areas are actively seeking solutions, today in the autumn after the end of the heat to talk about the sewage plant insulation problem.

In the existing sewage plant insulation, one is to do a whole plant to wrap the biological pool in the plant, plant materials generally used color steel plate and foam insulation plate material. Because the span of biological ponds is relatively large, it is necessary to build large span workshops. Thermal insulation board material weight is larger, the factory will use a large number of I-steel as structural support, and the overall investment is larger. From the operation effect, the thermal insulation effect of this type of workshop is better, but in order to strengthen the thermal insulation effect, generally few windows will be opened, leaving only entrance and exit doors, and in view of the cost, the later covered workshop will not have a higher space height, leaving only a higher position.

During the winter, the indoor temperature of such a plant can be kept high, but because of the closed plant, the insulation board materials are bonded tightly, the steam generated on the surface of the bio-pool in winter can not be released into the air, and a large number of water condenses on the steel structure in the plant, and the environment in the plant is extremely poor. It is very difficult for employees to enter the workshop.

From the observation of the water temperature of the biochemical pond, there is no special increase in the overall water temperature after increasing the thermal insulation plant. From the operation data, the curve has no special increase. The following chart shows the water temperature change curve, in which the thermal insulation board plant was completed in June-July 2017.

In actual operation, the fully enclosed plant structure prevents the heat exchange between water temperature and ambient air temperature, and provides a certain thermal insulation effect for the biological pond of the sewage treatment plant. However, it brings an important problem. Because of the use of the fully enclosed plant, the roof cannot use the temperature of sunlight after the use of opaque panels. Especially in the northwest, the sunshine is strong, the sunshine temperature is relatively strong, but cannot be used during the spring part of the temperature, the General Factory temperature is lower than the outside, especially in the midday sunshine period, indoor and outdoor temperature can be 5-10 degrees centigrade. The water temperature of the fully enclosed workshop with the roof made of transparent materials such as sunlight panels can be increased by 2 ~ 3 C than that of the fully enclosed workshop with opaque materials.

Another commonly used method is winter usage and temporary insulation measures in summer. This is mainly carried out in the form of frame structure and detachable push and pull, including plastic greenhouses and other measures. These materials have poor wind resistance, snow pressure resistance, easy to damage, cannot achieve winter heat preservation.

Other measures to keep temperature include adding electric heating belt to the aeration pipeline of the sewage treatment plant, and doing insulation layer at the same time, and heating measures to put steam pipeline into the aeration tank, etc. But these are easy to damage, power consumption, energy consumption, installation after the use of poor results, have been eliminated.

The above is the specific situation of the sewage treatment plants with thermal insulation measures. From the situation of the sewage treatment plants with relevant operation data, the change of water temperature in the sewage treatment plants with thermal insulation measures will be slightly slower than that in previous years. The main reason is that the thermal insulation materials block the heat exchange between water temperature and air in the biological pond, resulting in the water temperature being vacant. The effect of gas slows down. The height of the biological pond is high enough for the sewage treatment plant with sunshine roof, and the thermal insulation effect in the biological pond is obvious. Attention should be paid to the influence of northern gale weather. But the temperature of the effluent itself is the main reason for the low water temperature. The construction of heat preservation measures can only slow down the change of water temperature with the change of temperature, and cannot fundamentally change the situation of low water temperature. However, because of the large energy consumption, the heating measures cannot be realized in the sewage treatment plant. More effective heating measures can be aimed at the time of each plant, such as the original use of surface explosion machine, can be changed to bottom aeration, make full use of the heat of compressed air; the use of air pipes for small-scale heating and so on.

The measures of heating up sewage put forward in some areas are basically difficult to achieve in the case of municipal sewage treatment plant. The following is a rough calculation of heating insulation for a small sewage treatment plant.

The daily treatment capacity of a sewage treatment plant is about 9000 tons/day, which is affected by the temperature changes in the four seasons in the north. According to the field monitoring, during the winter operation period, the water temperature in A2O pond dropped to 15 C from October to December, and the lowest operating temperature was 10~12 C, which is far from the temperature range. The optimum temperature for biological reaction is far lower than that of microorganism. In order to achieve the best reaction temperature, the calculation of temperature rise is carried out.

In order to ensure good heat dissipation and heating effect, DN100-DN200 stainless steel pipe is recommended to be used for laying in order to enter the aeration tank daily. The water temperature can be raised by 10 C. At present, the daily water treatment capacity is calculated at 9000 tons, and 1 ton of water needs 1000 calories per day for one time.

9000 x 1000 x 10=90000000 =9000 card

Considering the heat loss of the pipeline and the configuration of the steam boiler, a boiler of 120 million calories and a boiler of 600 000 calories per ton are needed.

12000 tons / 60=200 tons

So at this stage, we need about 200 tons of boilers per day to heat the A2O pool. Considering the long-term capacity of more than 10,000 tons per day, we should configure about 250 tons of boilers.

From this rough calculation, it can be seen that heating sewage is extremely unrealistic, because the sewage plant itself is in a short time, in a small space to complete pollution control. In this case, heating will certainly lead to a large amount of energy consumption, and it is a very huge energy consumption, which makes the energy saving and consumption reduction of the sewage plant become an empty talk.

Seen from the existing thermal insulation management measures of sewage plants, the thermal insulation and heating measures of sewage plants will change little in winter operation and management of sewage plants, and even cause difficulties in operation and management. Therefore, in operation and management of sewage plants, the potential of winter process management should be further tapped, rather than relying on physics. The correct management concept of sewage treatment lies in the increase of facilities, the understanding of biological treatment capacity of sewage plants, the rational formulation of operation and management measures, the establishment of reasonable drainage standards, the recognition and acceptance of the laws of nature, rather than the imposition of man-made will on nature.