Many wastewater- and waste-treatment processes, together with other industrial activities generate liquid or semi-liquid waste streams. These can range from relatively innocuous dirty water to highly contaminated slurry containing heavy metals or high-risk biological material. Because of their liquid nature, these waste streams are often of a significant volume, which creates practical and financial challenges for storage, handling, and disposal.

To reduce these costs and improve the environmental footprint of their activities, many companies are looking for practical and efficient ways to reduce the volume of these waste streams. In turn this reduces the necessary storage and handling capacity, as well as reducing transport and disposal costs, resulting in less waste and a lower carbon footprint. Reducing the volume of these waste streams results in both financial and environmental benefits.

Evaporation is an efficient way of reducing the volume of effluents and wastes. HRS evaporation systems raise effluent, digestate or liquid waste to its boiling point so that water is evaporated and then condensed, thereby obtaining a concentrated end product and water. Forced recirculation uses a pump to send the product through the evaporator at high speeds, ensuring that heat transfer rates remain high, and the negative effects of fouling are limited.

Types of evaporation

There are three main types of evaporation system which can be utilized to reduce the volume of liquid waste streams:

Multi-effect evaporation

These systems combine various evaporation stages. The evaporated steam obtained from a previous stage is used as the thermal energy source for the resulting stage. Multiple stages can be combined to reduce the energy consumption needed for the total amount of water evaporated.

Mechanical vapor recompression (MVR)

In these systems, an additional compressor is used to increase the pressure and temperature of the water vapor or steam, which also provides the thermal energy source for the evaporation process. The only additional energy required is the electricity to power the compressor. This replaces the thermal energy used for evaporation with electrical energy and therefore increases efficiency.

Thermal vapor recompression (TVR) systems

When configured in a TVR setup, high pressure boiler steam is combined with the recovered (evaporated) low pressure steam in a thermocompressor. This maximizes the use of the recovered steam and provides considerable energy savings when compared with the use of boiler steam alone.

HRS evaporation and concentration systems

HRS evaporation systems are frequently integrated with waste heat sources to achieve an effective and sustainable process, which maximizes energy efficiency and reduces running costs. Using its 40 years of experience, HRS now offers a range of evaporation systems, although bespoke solutions are also available.

HRS corrugated tube evaporation systems

These are designed for the evaporation of low viscosity effluents with reduced particle size, like wastewater, brines, and effluents with low concentrations of organic solids. These systems utilize HRS K Series corrugated heat exchangers as evaporator modules, providing high heat transfer and good resistance against fouling.

HRS scraped surface evaporation systems

When concentrating fluids with elevated viscosities (which lowers heat transfer) or those which have a higher fouling risk, such as organic solutions with high dry matter concentration, HRS uses its HRS Unicus Series of reciprocating scraped-surface heat exchangers for evaporation systems.

HRS Digestate Concentration System

The HRS Digestate Concentration System (DCS) is specifically designed to reduce the volume of digestate from anaerobic digestion (AD) systems. In most situations the process utilizes surplus heat from the CHP engine. The DCS works by superheating digestate in a vacuum to facilitate concentration, using evaporation to significantly reduce digestate volumes while, at the same time, increasing the nutrient content and commercial value.

The HRS DCS is a multi-effect system (see above), in which the steam produced from this first heating cycle is re-used as the heating media for the second, and subsequent, effects. The number of effects is determined by the level of dry solids required, and the amount of spare heat available, up to a maximum of four cycles. After the final effect, the steam is condensed back into water and can then be used to dilute feedstock going into the front end of the digester, creating a completely closed loop system. The DCS is wholly self-sufficient – no energy or water is brought in or wasted, and everything is re-used.

To learn how HRS’ range of heat exchangers, evaporators and waste treatment systems can help you to manage your organic waste streams, visit HRS Heat Exchangers on stand 4409 at WEFTEC, at The Ernest N. Morial Convention Center in New Orleans, LA on 8-10^th October 2022.

For sales enquiries, please contact:

info@us.hrs-he.com

+1 (770) 726 3540

For media enquiries about HRS Heat Exchangers please contact:

Yenni Maelianawati, Senior Marketing Manager

Tel: +44 (0)1923 232 335

Email for publications: info@us.hrs-he.com

www.hrs-heatexchangers.com

Release issued by GloHouse Media: Bev Small, bev.small@glohouse.co.uk, Tel: +44(0)1223 872239 / +44(0)7901 841491

Our Ref.: hrs-ep-220704-a-ws